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 $194.52   9.823%   $213.6277   $213.63   $213.65   $213.60  
  Purchase #2 $181.73   8.581%   $197.3243   $197.32   $197.30   $197.30  
  Purchase #3 $33.73   8.500%   $36.5971   $36.60   $36.60   $36.60  
  Purchase #4 $164.50   11.843%   $183.9817   $183.98   $184.00   $184.00  
  Purchase #5 $181.80   11.557%   $202.8106   $202.81   $202.80   $202.80  
  Purchase #6 $130.59   11.826%   $146.0336   $146.03   $146.05   $146.00  
  Purchase #7 $22.66   12.388%   $25.4671   $25.47   $25.45   $25.50  
  7 purchase totals = $909.53       $1,005.8421   $1,005.84   $1,005.85   $1,005.80