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 $56.80   9.873%   $62.4079   $62.41   $62.40   $62.40  
  Purchase #2 $108.44   12.342%   $121.8237   $121.82   $121.80   $121.80  
  Purchase #3 $206.34   9.275%   $225.478   $225.48   $225.50   $225.50  
  Purchase #4 $61.76   13.222%   $69.9259   $69.93   $69.95   $69.90  
  Purchase #5 $239.94   5.710%   $253.6406   $253.64   $253.65   $253.60  
  Purchase #6 $29.62   13.318%   $33.5648   $33.56   $33.55   $33.60  
  Purchase #7 $216.47   13.142%   $244.9185   $244.92   $244.90   $244.90  
  7 purchase totals = $919.37       $1,011.7594   $1,011.76   $1,011.75   $1,011.70