Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.66   5.114%   $192.0012   $192.00   $192.00   $192.00  
  Purchase #2 $138.97   12.730%   $156.6609   $156.66   $156.65   $156.70  
  Purchase #3 $119.49   13.428%   $135.5351   $135.54   $135.55   $135.50  
  Purchase #4 $170.67   13.279%   $193.3333   $193.33   $193.35   $193.30  
  Purchase #5 $187.93   11.412%   $209.3766   $209.38   $209.40   $209.40  
  Purchase #6 $185.43   9.400%   $202.8604   $202.86   $202.85   $202.90  
  Purchase #7 $174.38   11.683%   $194.7528   $194.75   $194.75   $194.80  
  7 purchase totals = $1,159.53       $1,284.5203   $1,284.52   $1,284.55   $1,284.60