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 $86.64   11.521%   $96.6218   $96.62   $96.60   $96.60  
  Purchase #2 $248.39   5.258%   $261.4503   $261.45   $261.45   $261.50  
  Purchase #3 $204.31   6.678%   $217.9538   $217.95   $217.95   $218.00  
  Purchase #4 $236.66   4.211%   $246.6258   $246.63   $246.65   $246.60  
  Purchase #5 $57.66   5.419%   $60.7846   $60.78   $60.80   $60.80  
  Purchase #6 $165.26   3.198%   $170.545   $170.55   $170.55   $170.50  
  Purchase #7 $173.98   11.351%   $193.7285   $193.73   $193.75   $193.70  
  7 purchase totals = $1,172.90       $1,247.7098   $1,247.71   $1,247.75   $1,247.70