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 $34.97   4.114%   $36.4087   $36.41   $36.40   $36.40  
  Purchase #2 $110.62   5.561%   $116.7716   $116.77   $116.75   $116.80  
  Purchase #3 $148.62   6.487%   $158.261   $158.26   $158.25   $158.30  
  Purchase #4 $218.72   3.154%   $225.6184   $225.62   $225.60   $225.60  
  Purchase #5 $188.88   7.863%   $203.7316   $203.73   $203.75   $203.70  
  Purchase #6 $22.92   3.411%   $23.7018   $23.70   $23.70   $23.70  
  Purchase #7 $174.30   9.368%   $190.6284   $190.63   $190.65   $190.60  
  7 purchase totals = $899.03       $955.1215   $955.12   $955.10   $955.10