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 $124.95   8.873%   $136.0368   $136.04   $136.05   $136.00  
  Purchase #2 $193.86   10.274%   $213.7772   $213.78   $213.80   $213.80  
  Purchase #3 $214.53   3.301%   $221.6116   $221.61   $221.60   $221.60  
  Purchase #4 $101.81   10.265%   $112.2608   $112.26   $112.25   $112.30  
  Purchase #5 $234.73   6.185%   $249.2481   $249.25   $249.25   $249.20  
  Purchase #6 $245.74   9.255%   $268.4832   $268.48   $268.50   $268.50  
  Purchase #7 $60.41   3.465%   $62.5032   $62.50   $62.50   $62.50  
  7 purchase totals = $1,176.03       $1,263.9209   $1,263.92   $1,263.95   $1,263.90