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 $84.47   13.260%   $95.6707   $95.67   $95.65   $95.70  
  Purchase #2 $32.53   9.211%   $35.5263   $35.53   $35.55   $35.50  
  Purchase #3 $238.55   9.560%   $261.3554   $261.36   $261.35   $261.40  
  Purchase #4 $70.58   9.667%   $77.403   $77.40   $77.40   $77.40  
  Purchase #5 $163.93   3.747%   $170.0725   $170.07   $170.05   $170.10  
  Purchase #6 $37.93   13.776%   $43.1552   $43.16   $43.15   $43.20  
  Purchase #7 $243.94   10.227%   $268.8877   $268.89   $268.90   $268.90  
  7 purchase totals = $871.93       $952.0708   $952.08   $952.05   $952.20