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 $237.62   3.319%   $245.5066   $245.51   $245.50   $245.50  
  Purchase #2 $42.56   13.435%   $48.2779   $48.28   $48.30   $48.30  
  Purchase #3 $100.61   13.473%   $114.1652   $114.17   $114.15   $114.20  
  Purchase #4 $64.79   12.249%   $72.7261   $72.73   $72.75   $72.70  
  Purchase #5 $222.56   7.681%   $239.6548   $239.65   $239.65   $239.70  
  Purchase #6 $236.94   5.467%   $249.8935   $249.89   $249.90   $249.90  
  Purchase #7 $68.51   9.473%   $75   $75.00   $75.00   $75.00  
  7 purchase totals = $973.59       $1,045.2241   $1,045.23   $1,045.25   $1,045.30