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 $234.84   6.354%   $249.7617   $249.76   $249.75   $249.80  
  Purchase #2 $164.93   12.382%   $185.3516   $185.35   $185.35   $185.40  
  Purchase #3 $233.27   11.546%   $260.2034   $260.20   $260.20   $260.20  
  Purchase #4 $202.58   9.191%   $221.1991   $221.20   $221.20   $221.20  
  Purchase #5 $91.75   4.339%   $95.731   $95.73   $95.75   $95.70  
  Purchase #6 $202.37   12.219%   $227.0976   $227.10   $227.10   $227.10  
  Purchase #7 $241.26   9.148%   $263.3305   $263.33   $263.35   $263.30  
  7 purchase totals = $1,371.00       $1,502.6749   $1,502.67   $1,502.70   $1,502.70