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 $183.97   11.707%   $205.5074   $205.51   $205.50   $205.50  
  Purchase #2 $245.89   13.533%   $279.1663   $279.17   $279.15   $279.20  
  Purchase #3 $63.42   4.571%   $66.3189   $66.32   $66.30   $66.30  
  Purchase #4 $104.63   9.231%   $114.2884   $114.29   $114.30   $114.30  
  Purchase #5 $29.36   9.562%   $32.1674   $32.17   $32.15   $32.20  
  Purchase #6 $220.61   3.771%   $228.9292   $228.93   $228.95   $228.90  
  Purchase #7 $106.26   13.366%   $120.4627   $120.46   $120.45   $120.50  
  7 purchase totals = $954.14       $1,046.8403   $1,046.85   $1,046.80   $1,046.90