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 $52.68   7.215%   $56.4809   $56.48   $56.50   $56.50  
  Purchase #2 $223.45   7.201%   $239.5406   $239.54   $239.55   $239.50  
  Purchase #3 $93.47   7.717%   $100.6831   $100.68   $100.70   $100.70  
  Purchase #4 $117.38   7.406%   $126.0732   $126.07   $126.05   $126.10  
  Purchase #5 $223.79   6.161%   $237.5777   $237.58   $237.60   $237.60  
  Purchase #6 $224.73   8.350%   $243.495   $243.50   $243.50   $243.50  
  Purchase #7 $215.81   9.540%   $236.3983   $236.40   $236.40   $236.40  
  7 purchase totals = $1,151.31       $1,240.2488   $1,240.25   $1,240.30   $1,240.30