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 $196.53   9.657%   $215.5089   $215.51   $215.50   $215.50  
  Purchase #2 $201.53   13.132%   $227.9949   $227.99   $228.00   $228.00  
  Purchase #3 $112.54   5.283%   $118.4855   $118.49   $118.50   $118.50  
  Purchase #4 $227.79   3.720%   $236.2638   $236.26   $236.25   $236.30  
  Purchase #5 $144.70   13.571%   $164.3372   $164.34   $164.35   $164.30  
  Purchase #6 $195.82   11.165%   $217.6833   $217.68   $217.70   $217.70  
  Purchase #7 $106.44   9.177%   $116.208   $116.21   $116.20   $116.20  
  7 purchase totals = $1,185.35       $1,296.4816   $1,296.48   $1,296.50   $1,296.50