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 $67.57   6.660%   $72.0702   $72.07   $72.05   $72.10  
  Purchase #2 $69.81   5.597%   $73.7173   $73.72   $73.70   $73.70  
  Purchase #3 $53.88   13.553%   $61.1824   $61.18   $61.20   $61.20  
  Purchase #4 $106.88   8.808%   $116.294   $116.29   $116.30   $116.30  
  Purchase #5 $178.74   3.617%   $185.205   $185.21   $185.20   $185.20  
  Purchase #6 $89.63   8.132%   $96.9187   $96.92   $96.90   $96.90  
  Purchase #7 $227.75   8.345%   $246.7557   $246.76   $246.75   $246.80  
  7 purchase totals = $794.26       $852.1433   $852.15   $852.10   $852.20