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 $66.72   13.337%   $75.6184   $75.62   $75.60   $75.60  
  Purchase #2 $110.42   13.799%   $125.6569   $125.66   $125.65   $125.70  
  Purchase #3 $125.60   11.844%   $140.4761   $140.48   $140.50   $140.50  
  Purchase #4 $158.95   10.443%   $175.5491   $175.55   $175.55   $175.50  
  Purchase #5 $85.98   11.815%   $96.1385   $96.14   $96.15   $96.10  
  Purchase #6 $89.37   5.364%   $94.1638   $94.16   $94.15   $94.20  
  Purchase #7 $246.88   7.485%   $265.359   $265.36   $265.35   $265.40  
  7 purchase totals = $883.92       $972.9618   $972.97   $972.95   $973.00