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 $237.83   12.480%   $267.5112   $267.51   $267.50   $267.50  
  Purchase #2 $209.82   10.632%   $232.1281   $232.13   $232.15   $232.10  
  Purchase #3 $242.99   6.808%   $259.5328   $259.53   $259.55   $259.50  
  Purchase #4 $236.73   3.314%   $244.5752   $244.58   $244.60   $244.60  
  Purchase #5 $50.34   8.474%   $54.6058   $54.61   $54.60   $54.60  
  Purchase #6 $41.97   12.151%   $47.0698   $47.07   $47.05   $47.10  
  Purchase #7 $223.26   7.354%   $239.6785   $239.68   $239.70   $239.70  
  7 purchase totals = $1,242.94       $1,345.1014   $1,345.11   $1,345.15   $1,345.10