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 $61.75   4.599%   $64.5899   $64.59   $64.60   $64.60  
  Purchase #2 $62.61   6.399%   $66.6164   $66.62   $66.60   $66.60  
  Purchase #3 $197.26   10.563%   $218.0966   $218.10   $218.10   $218.10  
  Purchase #4 $205.80   13.777%   $234.1531   $234.15   $234.15   $234.20  
  Purchase #5 $168.37   4.778%   $176.4147   $176.41   $176.40   $176.40  
  Purchase #6 $112.58   3.603%   $116.6363   $116.64   $116.65   $116.60  
  Purchase #7 $40.86   8.188%   $44.2056   $44.21   $44.20   $44.20  
  7 purchase totals = $849.23       $920.7126   $920.72   $920.70   $920.70