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 $241.79   9.405%   $264.5303   $264.53   $264.55   $264.50  
  Purchase #2 $67.63   11.453%   $75.3757   $75.38   $75.40   $75.40  
  Purchase #3 $188.33   11.738%   $210.4362   $210.44   $210.45   $210.40  
  Purchase #4 $231.63   3.423%   $239.5587   $239.56   $239.55   $239.60  
  Purchase #5 $215.57   11.647%   $240.6774   $240.68   $240.70   $240.70  
  Purchase #6 $173.87   3.102%   $179.2634   $179.26   $179.25   $179.30  
  Purchase #7 $14.83   10.269%   $16.3529   $16.35   $16.35   $16.40  
  7 purchase totals = $1,133.65       $1,226.1946   $1,226.20   $1,226.25   $1,226.30