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 $82.95   13.613%   $94.242   $94.24   $94.25   $94.20  
  Purchase #2 $8.88   11.147%   $9.8699   $9.87   $9.85   $9.90  
  Purchase #3 $185.93   4.207%   $193.7521   $193.75   $193.75   $193.80  
  Purchase #4 $108.89   13.802%   $123.919   $123.92   $123.90   $123.90  
  Purchase #5 $231.32   13.689%   $262.9854   $262.99   $263.00   $263.00  
  Purchase #6 $81.98   10.446%   $90.5436   $90.54   $90.55   $90.50  
  Purchase #7 $56.60   10.649%   $62.6273   $62.63   $62.65   $62.60  
  7 purchase totals = $756.55       $837.9393   $837.94   $837.95   $837.90