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 $224.47   12.148%   $251.7386   $251.74   $251.75   $251.70  
  Purchase #2 $56.67   10.348%   $62.5342   $62.53   $62.55   $62.50  
  Purchase #3 $127.43   5.486%   $134.4208   $134.42   $134.40   $134.40  
  Purchase #4 $209.47   3.626%   $217.0654   $217.07   $217.05   $217.10  
  Purchase #5 $195.94   8.777%   $213.1377   $213.14   $213.15   $213.10  
  Purchase #6 $216.39   6.714%   $230.9184   $230.92   $230.90   $230.90  
  Purchase #7 $191.63   11.393%   $213.4624   $213.46   $213.45   $213.50  
  7 purchase totals = $1,222.00       $1,323.2775   $1,323.28   $1,323.25   $1,323.20