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 $163.68   6.211%   $173.8462   $173.85   $173.85   $173.80  
  Purchase #2 $180.63   8.345%   $195.7036   $195.70   $195.70   $195.70  
  Purchase #3 $5.75   8.220%   $6.2227   $6.22   $6.20   $6.20  
  Purchase #4 $208.57   6.730%   $222.6068   $222.61   $222.60   $222.60  
  Purchase #5 $75.97   6.234%   $80.706   $80.71   $80.70   $80.70  
  Purchase #6 $125.67   11.475%   $140.0906   $140.09   $140.10   $140.10  
  Purchase #7 $25.93   4.730%   $27.1565   $27.16   $27.15   $27.20  
  7 purchase totals = $786.20       $846.3324   $846.34   $846.30   $846.30