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 $104.75   13.527%   $118.9195   $118.92   $118.90   $118.90  
  Purchase #2 $193.96   8.152%   $209.7716   $209.77   $209.75   $209.80  
  Purchase #3 $162.99   13.604%   $185.1632   $185.16   $185.15   $185.20  
  Purchase #4 $133.81   6.316%   $142.2614   $142.26   $142.25   $142.30  
  Purchase #5 $239.47   4.602%   $250.4904   $250.49   $250.50   $250.50  
  Purchase #6 $8.42   8.350%   $9.1231   $9.12   $9.10   $9.10  
  Purchase #7 $150.59   7.111%   $161.2985   $161.30   $161.30   $161.30  
  7 purchase totals = $993.99       $1,077.0277   $1,077.02   $1,076.95   $1,077.10