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 $49.95   3.194%   $51.5454   $51.55   $51.55   $51.50  
  Purchase #2 $236.83   5.388%   $249.5904   $249.59   $249.60   $249.60  
  Purchase #3 $104.76   9.618%   $114.8358   $114.84   $114.85   $114.80  
  Purchase #4 $54.37   6.574%   $57.9443   $57.94   $57.95   $57.90  
  Purchase #5 $210.60   8.594%   $228.699   $228.70   $228.70   $228.70  
  Purchase #6 $96.97   13.552%   $110.1114   $110.11   $110.10   $110.10  
  Purchase #7 $190.32   10.608%   $210.5091   $210.51   $210.50   $210.50  
  7 purchase totals = $943.80       $1,023.2354   $1,023.24   $1,023.25   $1,023.10