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 $8.54   11.659%   $9.5357   $9.54   $9.55   $9.50  
  Purchase #2 $247.69   6.403%   $263.5496   $263.55   $263.55   $263.50  
  Purchase #3 $75.60   13.243%   $85.6117   $85.61   $85.60   $85.60  
  Purchase #4 $236.68   3.638%   $245.2904   $245.29   $245.30   $245.30  
  Purchase #5 $105.74   10.566%   $116.9125   $116.91   $116.90   $116.90  
  Purchase #6 $155.57   11.698%   $173.7686   $173.77   $173.75   $173.80  
  Purchase #7 $53.73   5.828%   $56.8614   $56.86   $56.85   $56.90  
  7 purchase totals = $883.55       $951.5299   $951.53   $951.50   $951.50