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 $55.61   12.462%   $62.5401   $62.54   $62.55   $62.50  
  Purchase #2 $53.82   12.174%   $60.372   $60.37   $60.35   $60.40  
  Purchase #3 $250.81   13.481%   $284.6217   $284.62   $284.60   $284.60  
  Purchase #4 $185.55   7.407%   $199.2937   $199.29   $199.30   $199.30  
  Purchase #5 $54.95   11.638%   $61.3451   $61.35   $61.35   $61.30  
  Purchase #6 $19.25   9.654%   $21.1084   $21.11   $21.10   $21.10  
  Purchase #7 $236.37   10.204%   $260.4892   $260.49   $260.50   $260.50  
  7 purchase totals = $856.36       $949.7702   $949.77   $949.75   $949.70