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 $62.87   3.188%   $64.8743   $64.87   $64.85   $64.90  
  Purchase #2 $213.90   5.143%   $224.9009   $224.90   $224.90   $224.90  
  Purchase #3 $207.80   13.475%   $235.8011   $235.80   $235.80   $235.80  
  Purchase #4 $14.87   12.754%   $16.7665   $16.77   $16.75   $16.80  
  Purchase #5 $166.72   9.219%   $182.0899   $182.09   $182.10   $182.10  
  Purchase #6 $192.63   9.821%   $211.5482   $211.55   $211.55   $211.50  
  Purchase #7 $59.53   6.347%   $63.3084   $63.31   $63.30   $63.30  
  7 purchase totals = $918.32       $999.2893   $999.29   $999.25   $999.30