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 $74.44   13.560%   $84.5341   $84.53   $84.55   $84.50  
  Purchase #2 $33.63   3.827%   $34.917   $34.92   $34.90   $34.90  
  Purchase #3 $84.88   9.509%   $92.9512   $92.95   $92.95   $93.00  
  Purchase #4 $175.73   10.783%   $194.679   $194.68   $194.70   $194.70  
  Purchase #5 $194.59   7.652%   $209.48   $209.48   $209.50   $209.50  
  Purchase #6 $5.80   8.486%   $6.2922   $6.29   $6.30   $6.30  
  Purchase #7 $96.98   3.114%   $100   $100.00   $100.00   $100.00  
  7 purchase totals = $666.05       $722.8535   $722.85   $722.90   $722.90