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 $66.75   11.245%   $74.256   $74.26   $74.25   $74.30  
  Purchase #2 $113.47   10.852%   $125.7838   $125.78   $125.80   $125.80  
  Purchase #3 $5.81   7.166%   $6.2263   $6.23   $6.25   $6.20  
  Purchase #4 $5.97   4.394%   $6.2323   $6.23   $6.25   $6.20  
  Purchase #5 $217.29   9.549%   $238.039   $238.04   $238.05   $238.00  
  Purchase #6 $56.49   8.175%   $61.1081   $61.11   $61.10   $61.10  
  Purchase #7 $163.85   5.676%   $173.1501   $173.15   $173.15   $173.20  
  7 purchase totals = $629.63       $684.7956   $684.80   $684.85   $684.80