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 $153.42   5.601%   $162.0131   $162.01   $162.00   $162.00  
  Purchase #2 $185.75   8.193%   $200.9685   $200.97   $200.95   $201.00  
  Purchase #3 $127.25   13.143%   $143.9745   $143.97   $143.95   $144.00  
  Purchase #4 $95.61   10.689%   $105.8298   $105.83   $105.85   $105.80  
  Purchase #5 $156.99   7.336%   $168.5068   $168.51   $168.50   $168.50  
  Purchase #6 $70.28   3.325%   $72.6168   $72.62   $72.60   $72.60  
  Purchase #7 $60.66   12.437%   $68.2043   $68.20   $68.20   $68.20  
  7 purchase totals = $849.96       $922.1138   $922.11   $922.05   $922.10