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 $201.56   3.206%   $208.022   $208.02   $208.00   $208.00  
  Purchase #2 $110.36   7.784%   $118.9504   $118.95   $118.95   $119.00  
  Purchase #3 $116.92   3.389%   $120.8824   $120.88   $120.90   $120.90  
  Purchase #4 $63.51   11.163%   $70.5996   $70.60   $70.60   $70.60  
  Purchase #5 $33.26   6.462%   $35.4093   $35.41   $35.40   $35.40  
  Purchase #6 $57.64   10.335%   $63.5971   $63.60   $63.60   $63.60  
  Purchase #7 $196.93   7.421%   $211.5442   $211.54   $211.55   $211.50  
  7 purchase totals = $780.18       $829.0050   $829.00   $829.00   $829.00