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 $83.90   12.304%   $94.2231   $94.22   $94.20   $94.20  
  Purchase #2 $231.86   12.136%   $259.9985   $260.00   $260.00   $260.00  
  Purchase #3 $231.35   7.723%   $249.2172   $249.22   $249.20   $249.20  
  Purchase #4 $130.78   6.578%   $139.3827   $139.38   $139.40   $139.40  
  Purchase #5 $110.49   7.612%   $118.9005   $118.90   $118.90   $118.90  
  Purchase #6 $49.71   9.426%   $54.3957   $54.40   $54.40   $54.40  
  Purchase #7 $33.68   9.131%   $36.7553   $36.76   $36.75   $36.80  
  7 purchase totals = $871.77       $952.8730   $952.88   $952.85   $952.90