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 $98.87   4.116%   $102.9395   $102.94   $102.95   $102.90  
  Purchase #2 $103.61   4.129%   $107.8881   $107.89   $107.90   $107.90  
  Purchase #3 $118.25   3.792%   $122.734   $122.73   $122.75   $122.70  
  Purchase #4 $176.83   3.452%   $182.9342   $182.93   $182.95   $182.90  
  Purchase #5 $211.68   10.426%   $233.7498   $233.75   $233.75   $233.70  
  Purchase #6 $92.95   4.269%   $96.918   $96.92   $96.90   $96.90  
  Purchase #7 $6.76   3.247%   $6.9795   $6.98   $7.00   $7.00  
  7 purchase totals = $808.95       $854.1431   $854.14   $854.20   $854.00