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 $63.53   5.340%   $66.9225   $66.92   $66.90   $66.90  
  Purchase #2 $247.78   4.375%   $258.6204   $258.62   $258.60   $258.60  
  Purchase #3 $189.82   10.618%   $209.9751   $209.98   $210.00   $210.00  
  Purchase #4 $100.70   4.674%   $105.4067   $105.41   $105.40   $105.40  
  Purchase #5 $72.77   5.553%   $76.8109   $76.81   $76.80   $76.80  
  Purchase #6 $146.72   11.473%   $163.5532   $163.55   $163.55   $163.60  
  Purchase #7 $95.76   8.855%   $104.2395   $104.24   $104.25   $104.20  
  7 purchase totals = $917.08       $985.5283   $985.53   $985.50   $985.50