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 $44.76   4.849%   $46.9304   $46.93   $46.95   $46.90  
  Purchase #2 $161.69   13.709%   $183.8561   $183.86   $183.85   $183.90  
  Purchase #3 $135.80   13.837%   $154.5906   $154.59   $154.60   $154.60  
  Purchase #4 $153.84   6.361%   $163.6258   $163.63   $163.65   $163.60  
  Purchase #5 $214.55   7.733%   $231.1412   $231.14   $231.15   $231.10  
  Purchase #6 $117.26   6.290%   $124.6357   $124.64   $124.65   $124.60  
  Purchase #7 $110.27   5.316%   $116.132   $116.13   $116.15   $116.10  
  7 purchase totals = $938.17       $1,020.9118   $1,020.92   $1,021.00   $1,020.80