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 $211.94   9.632%   $232.3541   $232.35   $232.35   $232.40  
  Purchase #2 $18.44   7.411%   $19.8066   $19.81   $19.80   $19.80  
  Purchase #3 $25.82   9.771%   $28.3429   $28.34   $28.35   $28.30  
  Purchase #4 $66.81   9.609%   $73.2298   $73.23   $73.25   $73.20  
  Purchase #5 $70.40   10.731%   $77.9546   $77.95   $77.95   $78.00  
  Purchase #6 $55.63   12.161%   $62.3952   $62.40   $62.40   $62.40  
  Purchase #7 $173.92   4.756%   $182.1916   $182.19   $182.20   $182.20  
  7 purchase totals = $622.96       $676.2748   $676.27   $676.30   $676.30