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 $51.93   9.726%   $56.9807   $56.98   $57.00   $57.00  
  Purchase #2 $132.63   8.384%   $143.7497   $143.75   $143.75   $143.70  
  Purchase #3 $183.66   5.767%   $194.2517   $194.25   $194.25   $194.30  
  Purchase #4 $211.33   7.290%   $226.736   $226.74   $226.75   $226.70  
  Purchase #5 $42.87   9.770%   $47.0584   $47.06   $47.05   $47.10  
  Purchase #6 $55.27   10.224%   $60.9208   $60.92   $60.90   $60.90  
  Purchase #7 $134.91   5.559%   $142.4096   $142.41   $142.40   $142.40  
  7 purchase totals = $812.60       $872.1069   $872.11   $872.10   $872.10