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 $84.77   13.225%   $95.9808   $95.98   $96.00   $96.00  
  Purchase #2 $70.53   10.143%   $77.6839   $77.68   $77.70   $77.70  
  Purchase #3 $62.47   8.443%   $67.7443   $67.74   $67.75   $67.70  
  Purchase #4 $125.33   5.306%   $131.98   $131.98   $132.00   $132.00  
  Purchase #5 $73.62   3.250%   $76.0127   $76.01   $76.00   $76.00  
  Purchase #6 $198.54   7.738%   $213.903   $213.90   $213.90   $213.90  
  Purchase #7 $15.40   11.451%   $17.1635   $17.16   $17.15   $17.20  
  7 purchase totals = $630.66       $680.4682   $680.45   $680.50   $680.50