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 $66.25   3.598%   $68.6337   $68.63   $68.65   $68.60  
  Purchase #2 $248.70   4.252%   $259.2747   $259.27   $259.25   $259.30  
  Purchase #3 $216.96   10.586%   $239.9274   $239.93   $239.95   $239.90  
  Purchase #4 $106.97   11.577%   $119.3539   $119.35   $119.35   $119.40  
  Purchase #5 $107.96   8.112%   $116.7177   $116.72   $116.70   $116.70  
  Purchase #6 $215.55   5.517%   $227.4419   $227.44   $227.45   $227.40  
  Purchase #7 $18.73   13.408%   $21.2413   $21.24   $21.25   $21.20  
  7 purchase totals = $981.12       $1,052.5906   $1,052.58   $1,052.60   $1,052.50