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 $22.45   10.146%   $24.7278   $24.73   $24.75   $24.70  
  Purchase #2 $244.81   5.179%   $257.4887   $257.49   $257.50   $257.50  
  Purchase #3 $110.39   10.774%   $122.2834   $122.28   $122.30   $122.30  
  Purchase #4 $217.78   4.841%   $228.3227   $228.32   $228.30   $228.30  
  Purchase #5 $206.66   8.545%   $224.3191   $224.32   $224.30   $224.30  
  Purchase #6 $125.37   9.267%   $136.988   $136.99   $137.00   $137.00  
  Purchase #7 $27.45   6.447%   $29.2197   $29.22   $29.20   $29.20  
  7 purchase totals = $954.91       $1,023.3494   $1,023.35   $1,023.35   $1,023.30