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 $204.51   10.532%   $226.049   $226.05   $226.05   $226.00  
  Purchase #2 $85.86   10.308%   $94.7104   $94.71   $94.70   $94.70  
  Purchase #3 $29.82   3.291%   $30.8014   $30.80   $30.80   $30.80  
  Purchase #4 $129.77   11.251%   $144.3704   $144.37   $144.35   $144.40  
  Purchase #5 $21.26   9.141%   $23.2034   $23.20   $23.20   $23.20  
  Purchase #6 $115.66   8.624%   $125.6345   $125.63   $125.65   $125.60  
  Purchase #7 $102.48   11.136%   $113.8922   $113.89   $113.90   $113.90  
  7 purchase totals = $689.36       $758.6613   $758.65   $758.65   $758.60