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 $61.71   7.157%   $66.1266   $66.13   $66.15   $66.10  
  Purchase #2 $213.69   10.522%   $236.1745   $236.17   $236.15   $236.20  
  Purchase #3 $183.84   11.195%   $204.4209   $204.42   $204.40   $204.40  
  Purchase #4 $60.99   10.650%   $67.4854   $67.49   $67.50   $67.50  
  Purchase #5 $74.69   4.110%   $77.7598   $77.76   $77.75   $77.80  
  Purchase #6 $116.54   6.786%   $124.4484   $124.45   $124.45   $124.40  
  Purchase #7 $235.38   10.625%   $260.3891   $260.39   $260.40   $260.40  
  7 purchase totals = $946.84       $1,036.8047   $1,036.81   $1,036.80   $1,036.80