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 $53.95   8.152%   $58.348   $58.35   $58.35   $58.30  
  Purchase #2 $82.84   8.338%   $89.7472   $89.75   $89.75   $89.70  
  Purchase #3 $153.51   12.498%   $172.6957   $172.70   $172.70   $172.70  
  Purchase #4 $250.43   10.156%   $275.8637   $275.86   $275.85   $275.90  
  Purchase #5 $125.82   11.526%   $140.322   $140.32   $140.30   $140.30  
  Purchase #6 $101.99   6.643%   $108.7652   $108.77   $108.75   $108.80  
  Purchase #7 $63.89   6.626%   $68.1234   $68.12   $68.10   $68.10  
  7 purchase totals = $832.43       $913.8652   $913.87   $913.80   $913.80