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 $60.69   8.858%   $66.0659   $66.07   $66.05   $66.10  
  Purchase #2 $73.77   5.308%   $77.6857   $77.69   $77.70   $77.70  
  Purchase #3 $90.72   12.761%   $102.2968   $102.30   $102.30   $102.30  
  Purchase #4 $244.87   9.105%   $267.1654   $267.17   $267.15   $267.20  
  Purchase #5 $236.40   4.793%   $247.7307   $247.73   $247.75   $247.70  
  Purchase #6 $98.42   12.335%   $110.5601   $110.56   $110.55   $110.60  
  Purchase #7 $81.29   11.253%   $90.4376   $90.44   $90.45   $90.40  
  7 purchase totals = $886.16       $961.9422   $961.96   $961.95   $962.00