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 $20.73   7.332%   $22.2499   $22.25   $22.25   $22.20  
  Purchase #2 $13.62   4.427%   $14.223   $14.22   $14.20   $14.20  
  Purchase #3 $132.94   4.371%   $138.7508   $138.75   $138.75   $138.80  
  Purchase #4 $132.71   3.461%   $137.3031   $137.30   $137.30   $137.30  
  Purchase #5 $130.41   8.525%   $141.5275   $141.53   $141.55   $141.50  
  Purchase #6 $122.89   9.256%   $134.2647   $134.26   $134.25   $134.30  
  Purchase #7 $132.92   6.199%   $141.1597   $141.16   $141.15   $141.20  
  7 purchase totals = $686.22       $729.4787   $729.47   $729.45   $729.50