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 $221.98   12.475%   $249.672   $249.67   $249.65   $249.70  
  Purchase #2 $32.42   8.121%   $35.0528   $35.05   $35.05   $35.10  
  Purchase #3 $101.84   13.340%   $115.4255   $115.43   $115.45   $115.40  
  Purchase #4 $17.77   13.179%   $20.1119   $20.11   $20.10   $20.10  
  Purchase #5 $54.75   5.785%   $57.9173   $57.92   $57.90   $57.90  
  Purchase #6 $233.78   12.817%   $263.7436   $263.74   $263.75   $263.70  
  Purchase #7 $107.46   11.195%   $119.4901   $119.49   $119.50   $119.50  
  7 purchase totals = $770.00       $861.4132   $861.41   $861.40   $861.40