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 $242.79   7.593%   $261.225   $261.23   $261.25   $261.20  
  Purchase #2 $132.73   11.273%   $147.6927   $147.69   $147.70   $147.70  
  Purchase #3 $42.43   6.105%   $45.0204   $45.02   $45.00   $45.00  
  Purchase #4 $250.55   9.562%   $274.5076   $274.51   $274.50   $274.50  
  Purchase #5 $205.90   6.833%   $219.9691   $219.97   $219.95   $220.00  
  Purchase #6 $44.97   13.307%   $50.9542   $50.95   $50.95   $51.00  
  Purchase #7 $236.26   5.281%   $248.7369   $248.74   $248.75   $248.70  
  7 purchase totals = $1,155.63       $1,248.1059   $1,248.11   $1,248.10   $1,248.10