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 $174.61   12.223%   $195.9526   $195.95   $195.95   $196.00  
  Purchase #2 $14.40   11.358%   $16.0356   $16.04   $16.05   $16.00  
  Purchase #3 $18.44   6.165%   $19.5768   $19.58   $19.60   $19.60  
  Purchase #4 $186.27   11.769%   $208.1921   $208.19   $208.20   $208.20  
  Purchase #5 $106.98   9.741%   $117.4009   $117.40   $117.40   $117.40  
  Purchase #6 $231.84   13.406%   $262.9205   $262.92   $262.90   $262.90  
  Purchase #7 $121.45   13.120%   $137.3842   $137.38   $137.40   $137.40  
  7 purchase totals = $853.99       $957.4627   $957.46   $957.50   $957.50