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 $125.53   12.432%   $141.1359   $141.14   $141.15   $141.10  
  Purchase #2 $53.97   8.198%   $58.3945   $58.39   $58.40   $58.40  
  Purchase #3 $24.42   11.477%   $27.2227   $27.22   $27.20   $27.20  
  Purchase #4 $55.86   8.754%   $60.75   $60.75   $60.75   $60.80  
  Purchase #5 $140.34   10.842%   $155.5557   $155.56   $155.55   $155.60  
  Purchase #6 $81.96   8.774%   $89.1512   $89.15   $89.15   $89.20  
  Purchase #7 $68.68   11.433%   $76.5322   $76.53   $76.55   $76.50  
  7 purchase totals = $550.76       $608.7422   $608.74   $608.75   $608.80