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 $245.36   6.374%   $260.9992   $261.00   $261.00   $261.00  
  Purchase #2 $157.29   13.358%   $178.3008   $178.30   $178.30   $178.30  
  Purchase #3 $190.91   3.809%   $198.1818   $198.18   $198.20   $198.20  
  Purchase #4 $42.67   6.269%   $45.345   $45.35   $45.35   $45.30  
  Purchase #5 $203.90   13.730%   $231.8955   $231.90   $231.90   $231.90  
  Purchase #6 $84.66   9.334%   $92.5622   $92.56   $92.55   $92.60  
  Purchase #7 $233.47   11.848%   $261.1315   $261.13   $261.15   $261.10  
  7 purchase totals = $1,158.26       $1,268.4160   $1,268.42   $1,268.45   $1,268.40