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 $62.78   6.782%   $67.0377   $67.04   $67.05   $67.00  
  Purchase #2 $72.90   5.528%   $76.9299   $76.93   $76.95   $76.90  
  Purchase #3 $68.62   6.415%   $73.022   $73.02   $73.00   $73.00  
  Purchase #4 $211.46   11.659%   $236.1141   $236.11   $236.10   $236.10  
  Purchase #5 $153.96   7.852%   $166.0489   $166.05   $166.05   $166.00  
  Purchase #6 $87.28   11.674%   $97.4691   $97.47   $97.45   $97.50  
  Purchase #7 $59.83   10.659%   $66.2073   $66.21   $66.20   $66.20  
  7 purchase totals = $716.83       $782.8290   $782.83   $782.80   $782.70