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 $48.63   13.358%   $55.126   $55.13   $55.15   $55.10  
  Purchase #2 $182.78   4.785%   $191.526   $191.53   $191.55   $191.50  
  Purchase #3 $62.59   7.584%   $67.3368   $67.34   $67.35   $67.30  
  Purchase #4 $57.68   5.198%   $60.6782   $60.68   $60.70   $60.70  
  Purchase #5 $68.50   4.566%   $71.6277   $71.63   $71.65   $71.60  
  Purchase #6 $60.90   4.677%   $63.7483   $63.75   $63.75   $63.70  
  Purchase #7 $156.77   12.227%   $175.9383   $175.94   $175.95   $175.90  
  7 purchase totals = $637.85       $685.9813   $686.00   $686.10   $685.80