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 $242.69   9.185%   $264.9811   $264.98   $265.00   $265.00  
  Purchase #2 $23.46   5.196%   $24.679   $24.68   $24.70   $24.70  
  Purchase #3 $165.83   4.691%   $173.6091   $173.61   $173.60   $173.60  
  Purchase #4 $111.56   4.221%   $116.2689   $116.27   $116.25   $116.30  
  Purchase #5 $234.88   3.127%   $242.2247   $242.22   $242.20   $242.20  
  Purchase #6 $240.63   10.340%   $265.5111   $265.51   $265.50   $265.50  
  Purchase #7 $146.29   8.584%   $158.8475   $158.85   $158.85   $158.80  
  7 purchase totals = $1,165.34       $1,246.1214   $1,246.12   $1,246.10   $1,246.10