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 $231.92   12.749%   $261.4875   $261.49   $261.50   $261.50  
  Purchase #2 $197.36   3.846%   $204.9505   $204.95   $204.95   $205.00  
  Purchase #3 $206.47   13.442%   $234.2237   $234.22   $234.20   $234.20  
  Purchase #4 $248.26   5.625%   $262.2246   $262.22   $262.20   $262.20  
  Purchase #5 $223.69   11.402%   $249.1951   $249.20   $249.20   $249.20  
  Purchase #6 $172.83   9.427%   $189.1227   $189.12   $189.10   $189.10  
  Purchase #7 $241.62   6.352%   $256.9677   $256.97   $256.95   $257.00  
  7 purchase totals = $1,522.15       $1,658.1718   $1,658.17   $1,658.10   $1,658.20