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 $112.71   3.639%   $116.8115   $116.81   $116.80   $116.80  
  Purchase #2 $30.46   12.508%   $34.2699   $34.27   $34.25   $34.30  
  Purchase #3 $8.87   7.510%   $9.5361   $9.54   $9.55   $9.50  
  Purchase #4 $5.66   8.228%   $6.1257   $6.13   $6.15   $6.10  
  Purchase #5 $195.90   9.850%   $215.1962   $215.20   $215.20   $215.20  
  Purchase #6 $80.89   9.713%   $88.7468   $88.75   $88.75   $88.70  
  Purchase #7 $144.63   13.281%   $163.8383   $163.84   $163.85   $163.80  
  7 purchase totals = $579.12       $634.5245   $634.54   $634.55   $634.40