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 $65.56   10.111%   $72.1888   $72.19   $72.20   $72.20  
  Purchase #2 $84.47   10.426%   $93.2768   $93.28   $93.30   $93.30  
  Purchase #3 $59.76   10.433%   $65.9948   $65.99   $66.00   $66.00  
  Purchase #4 $227.39   4.491%   $237.6021   $237.60   $237.60   $237.60  
  Purchase #5 $212.61   11.249%   $236.5265   $236.53   $236.55   $236.50  
  Purchase #6 $150.50   8.622%   $163.4761   $163.48   $163.50   $163.50  
  Purchase #7 $190.42   10.671%   $210.7397   $210.74   $210.75   $210.70  
  7 purchase totals = $990.71       $1,079.8048   $1,079.81   $1,079.90   $1,079.80