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 $180.82   8.268%   $195.7702   $195.77   $195.75   $195.80  
  Purchase #2 $179.48   7.497%   $192.9356   $192.94   $192.95   $192.90  
  Purchase #3 $240.96   7.489%   $259.0055   $259.01   $259.00   $259.00  
  Purchase #4 $114.34   3.362%   $118.1841   $118.18   $118.20   $118.20  
  Purchase #5 $144.74   8.603%   $157.192   $157.19   $157.20   $157.20  
  Purchase #6 $232.93   11.221%   $259.0671   $259.07   $259.05   $259.10  
  Purchase #7 $78.89   4.665%   $82.5702   $82.57   $82.55   $82.60  
  7 purchase totals = $1,172.16       $1,264.7247   $1,264.73   $1,264.70   $1,264.80