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 $128.71   11.385%   $143.3636   $143.36   $143.35   $143.40  
  Purchase #2 $174.37   8.685%   $189.514   $189.51   $189.50   $189.50  
  Purchase #3 $231.95   4.733%   $242.9282   $242.93   $242.95   $242.90  
  Purchase #4 $167.67   13.618%   $190.5033   $190.50   $190.50   $190.50  
  Purchase #5 $207.99   8.797%   $226.2869   $226.29   $226.30   $226.30  
  Purchase #6 $128.80   7.553%   $138.5283   $138.53   $138.55   $138.50  
  Purchase #7 $236.41   10.373%   $260.9328   $260.93   $260.95   $260.90  
  7 purchase totals = $1,275.90       $1,392.0571   $1,392.05   $1,392.10   $1,392.00