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 $126.73   8.662%   $137.7074   $137.71   $137.70   $137.70  
  Purchase #2 $167.83   10.724%   $185.8281   $185.83   $185.85   $185.80  
  Purchase #3 $107.75   8.311%   $116.7051   $116.71   $116.70   $116.70  
  Purchase #4 $52.43   5.154%   $55.1322   $55.13   $55.15   $55.10  
  Purchase #5 $213.75   3.823%   $221.9217   $221.92   $221.90   $221.90  
  Purchase #6 $65.50   11.478%   $73.0181   $73.02   $73.00   $73.00  
  Purchase #7 $63.49   4.754%   $66.5083   $66.51   $66.50   $66.50  
  7 purchase totals = $797.48       $856.8209   $856.83   $856.80   $856.70