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 $84.61   9.295%   $92.4745   $92.47   $92.45   $92.50  
  Purchase #2 $96.56   7.560%   $103.8599   $103.86   $103.85   $103.90  
  Purchase #3 $40.93   9.787%   $44.9358   $44.94   $44.95   $44.90  
  Purchase #4 $185.57   5.176%   $195.1751   $195.18   $195.20   $195.20  
  Purchase #5 $239.35   4.282%   $249.599   $249.60   $249.60   $249.60  
  Purchase #6 $248.94   9.486%   $272.5544   $272.55   $272.55   $272.60  
  Purchase #7 $222.47   3.652%   $230.5946   $230.59   $230.60   $230.60  
  7 purchase totals = $1,118.43       $1,189.1933   $1,189.19   $1,189.20   $1,189.30