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 $201.51   11.262%   $224.2041   $224.20   $224.20   $224.20  
  Purchase #2 $250.84   9.598%   $274.9156   $274.92   $274.90   $274.90  
  Purchase #3 $247.53   5.590%   $261.3669   $261.37   $261.35   $261.40  
  Purchase #4 $190.92   9.610%   $209.2674   $209.27   $209.25   $209.30  
  Purchase #5 $180.75   9.708%   $198.2972   $198.30   $198.30   $198.30  
  Purchase #6 $149.34   4.605%   $156.2171   $156.22   $156.20   $156.20  
  Purchase #7 $46.99   8.785%   $51.1181   $51.12   $51.10   $51.10  
  7 purchase totals = $1,267.88       $1,375.3864   $1,375.40   $1,375.30   $1,375.40