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 $63.59   9.478%   $69.6171   $69.62   $69.60   $69.60  
  Purchase #2 $90.90   4.339%   $94.8442   $94.84   $94.85   $94.80  
  Purchase #3 $219.28   7.737%   $236.2457   $236.25   $236.25   $236.20  
  Purchase #4 $125.61   12.112%   $140.8239   $140.82   $140.80   $140.80  
  Purchase #5 $48.63   13.629%   $55.2578   $55.26   $55.25   $55.30  
  Purchase #6 $177.71   4.491%   $185.691   $185.69   $185.70   $185.70  
  Purchase #7 $200.64   10.318%   $221.342   $221.34   $221.35   $221.30  
  7 purchase totals = $926.36       $1,003.8217   $1,003.82   $1,003.80   $1,003.70