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 $228.57   7.732%   $246.243   $246.24   $246.25   $246.20  
  Purchase #2 $14.83   9.520%   $16.2418   $16.24   $16.25   $16.20  
  Purchase #3 $245.47   5.274%   $258.4161   $258.42   $258.40   $258.40  
  Purchase #4 $217.73   8.625%   $236.5092   $236.51   $236.50   $236.50  
  Purchase #5 $81.43   3.709%   $84.4502   $84.45   $84.45   $84.50  
  Purchase #6 $121.28   7.183%   $129.9915   $129.99   $130.00   $130.00  
  Purchase #7 $21.62   8.265%   $23.4069   $23.41   $23.40   $23.40  
  7 purchase totals = $930.93       $995.2587   $995.26   $995.25   $995.20