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 $43.42   6.842%   $46.3908   $46.39   $46.40   $46.40  
  Purchase #2 $106.50   9.806%   $116.9434   $116.94   $116.95   $116.90  
  Purchase #3 $119.28   4.162%   $124.2444   $124.24   $124.25   $124.20  
  Purchase #4 $64.62   3.346%   $66.7822   $66.78   $66.80   $66.80  
  Purchase #5 $245.93   7.587%   $264.5887   $264.59   $264.60   $264.60  
  Purchase #6 $149.81   6.399%   $159.3963   $159.40   $159.40   $159.40  
  Purchase #7 $53.76   7.224%   $57.6436   $57.64   $57.65   $57.60  
  7 purchase totals = $783.32       $835.9894   $835.98   $836.05   $835.90