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 $53.38   10.483%   $58.9758   $58.98   $59.00   $59.00  
  Purchase #2 $174.73   11.156%   $194.2229   $194.22   $194.20   $194.20  
  Purchase #3 $154.29   3.387%   $159.5158   $159.52   $159.50   $159.50  
  Purchase #4 $89.63   9.284%   $97.9512   $97.95   $97.95   $98.00  
  Purchase #5 $32.43   7.843%   $34.9735   $34.97   $34.95   $35.00  
  Purchase #6 $123.96   4.448%   $129.4737   $129.47   $129.45   $129.50  
  Purchase #7 $85.69   13.645%   $97.3824   $97.38   $97.40   $97.40  
  7 purchase totals = $714.11       $772.4953   $772.49   $772.45   $772.60