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 $83.27   3.769%   $86.4084   $86.41   $86.40   $86.40  
  Purchase #2 $199.56   7.663%   $214.8523   $214.85   $214.85   $214.90  
  Purchase #3 $119.54   5.234%   $125.7967   $125.80   $125.80   $125.80  
  Purchase #4 $207.89   4.749%   $217.7627   $217.76   $217.75   $217.80  
  Purchase #5 $48.87   11.712%   $54.5937   $54.59   $54.60   $54.60  
  Purchase #6 $90.28   12.338%   $101.4187   $101.42   $101.40   $101.40  
  Purchase #7 $119.88   13.465%   $136.0218   $136.02   $136.00   $136.00  
  7 purchase totals = $869.29       $936.8543   $936.85   $936.80   $936.90