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 $68.32   10.613%   $75.5708   $75.57   $75.55   $75.60  
  Purchase #2 $46.77   13.807%   $53.2275   $53.23   $53.25   $53.20  
  Purchase #3 $23.42   4.760%   $24.5348   $24.53   $24.55   $24.50  
  Purchase #4 $125.55   11.317%   $139.7585   $139.76   $139.75   $139.80  
  Purchase #5 $191.35   13.868%   $217.8864   $217.89   $217.90   $217.90  
  Purchase #6 $78.81   5.817%   $83.3944   $83.39   $83.40   $83.40  
  Purchase #7 $246.95   6.491%   $262.9795   $262.98   $263.00   $263.00  
  7 purchase totals = $781.17       $857.3519   $857.35   $857.40   $857.40