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 $44.94   12.615%   $50.6092   $50.61   $50.60   $50.60  
  Purchase #2 $72.88   5.114%   $76.6071   $76.61   $76.60   $76.60  
  Purchase #3 $117.89   12.288%   $132.3763   $132.38   $132.40   $132.40  
  Purchase #4 $45.33   8.865%   $49.3485   $49.35   $49.35   $49.30  
  Purchase #5 $175.62   4.634%   $183.7582   $183.76   $183.75   $183.80  
  Purchase #6 $64.30   4.216%   $67.0109   $67.01   $67.00   $67.00  
  Purchase #7 $112.79   10.313%   $124.422   $124.42   $124.40   $124.40  
  7 purchase totals = $633.75       $684.1322   $684.14   $684.10   $684.10