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 $217.44   10.843%   $241.017   $241.02   $241.00   $241.00  
  Purchase #2 $7.85   4.518%   $8.2047   $8.20   $8.20   $8.20  
  Purchase #3 $79.41   11.649%   $88.6605   $88.66   $88.65   $88.70  
  Purchase #4 $226.25   4.666%   $236.8068   $236.81   $236.80   $236.80  
  Purchase #5 $111.86   11.613%   $124.8503   $124.85   $124.85   $124.90  
  Purchase #6 $123.98   10.585%   $137.1033   $137.10   $137.10   $137.10  
  Purchase #7 $66.86   4.549%   $69.9015   $69.90   $69.90   $69.90  
  7 purchase totals = $833.65       $906.5441   $906.54   $906.50   $906.60