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 $55.95   6.589%   $59.6365   $59.64   $59.65   $59.60  
  Purchase #2 $26.70   11.193%   $29.6885   $29.69   $29.70   $29.70  
  Purchase #3 $209.68   12.404%   $235.6887   $235.69   $235.70   $235.70  
  Purchase #4 $119.67   5.716%   $126.5103   $126.51   $126.50   $126.50  
  Purchase #5 $174.36   11.780%   $194.8996   $194.90   $194.90   $194.90  
  Purchase #6 $169.35   13.232%   $191.7584   $191.76   $191.75   $191.80  
  Purchase #7 $51.44   7.584%   $55.3412   $55.34   $55.35   $55.30  
  7 purchase totals = $807.15       $893.5232   $893.53   $893.55   $893.50