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 $61.56   10.732%   $68.1666   $68.17   $68.15   $68.20  
  Purchase #2 $58.35   4.498%   $60.9746   $60.97   $60.95   $61.00  
  Purchase #3 $157.97   12.548%   $177.7921   $177.79   $177.80   $177.80  
  Purchase #4 $70.40   5.846%   $74.5156   $74.52   $74.50   $74.50  
  Purchase #5 $24.69   9.749%   $27.097   $27.10   $27.10   $27.10  
  Purchase #6 $121.83   8.117%   $131.7189   $131.72   $131.70   $131.70  
  Purchase #7 $236.33   7.448%   $253.9319   $253.93   $253.95   $253.90  
  7 purchase totals = $731.13       $794.1967   $794.20   $794.15   $794.20