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 $247.98   9.793%   $272.2647   $272.26   $272.25   $272.30  
  Purchase #2 $245.47   6.623%   $261.7275   $261.73   $261.75   $261.70  
  Purchase #3 $230.43   6.195%   $244.7051   $244.71   $244.70   $244.70  
  Purchase #4 $55.97   11.861%   $62.6086   $62.61   $62.60   $62.60  
  Purchase #5 $249.96   4.288%   $260.6783   $260.68   $260.70   $260.70  
  Purchase #6 $230.50   5.519%   $243.2213   $243.22   $243.20   $243.20  
  Purchase #7 $103.98   8.667%   $112.9919   $112.99   $113.00   $113.00  
  7 purchase totals = $1,364.29       $1,458.1974   $1,458.20   $1,458.20   $1,458.20