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 $67.54   11.321%   $75.1862   $75.19   $75.20   $75.20  
  Purchase #2 $121.62   10.382%   $134.2466   $134.25   $134.25   $134.20  
  Purchase #3 $244.38   12.460%   $274.8297   $274.83   $274.85   $274.80  
  Purchase #4 $26.81   12.591%   $30.1856   $30.19   $30.20   $30.20  
  Purchase #5 $65.71   9.656%   $72.055   $72.06   $72.05   $72.10  
  Purchase #6 $137.75   9.856%   $151.3266   $151.33   $151.35   $151.30  
  Purchase #7 $52.65   6.249%   $55.9401   $55.94   $55.95   $55.90  
  7 purchase totals = $716.46       $793.7698   $793.79   $793.85   $793.70