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 $127.35   6.844%   $136.0658   $136.07   $136.05   $136.10  
  Purchase #2 $213.42   11.805%   $238.6142   $238.61   $238.60   $238.60  
  Purchase #3 $183.62   12.412%   $206.4109   $206.41   $206.40   $206.40  
  Purchase #4 $245.57   9.177%   $268.106   $268.11   $268.10   $268.10  
  Purchase #5 $248.39   5.786%   $262.7618   $262.76   $262.75   $262.80  
  Purchase #6 $48.96   3.266%   $50.559   $50.56   $50.55   $50.60  
  Purchase #7 $234.41   9.531%   $256.7516   $256.75   $256.75   $256.80  
  7 purchase totals = $1,301.72       $1,419.2693   $1,419.27   $1,419.20   $1,419.40