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 $194.90   5.452%   $205.5259   $205.53   $205.55   $205.50  
  Purchase #2 $26.95   13.293%   $30.5325   $30.53   $30.55   $30.50  
  Purchase #3 $38.48   13.808%   $43.7933   $43.79   $43.80   $43.80  
  Purchase #4 $206.53   13.609%   $234.6367   $234.64   $234.65   $234.60  
  Purchase #5 $109.44   4.375%   $114.228   $114.23   $114.25   $114.20  
  Purchase #6 $23.82   8.157%   $25.763   $25.76   $25.75   $25.80  
  Purchase #7 $12.25   11.295%   $13.6336   $13.63   $13.65   $13.60  
  7 purchase totals = $612.37       $668.1130   $668.11   $668.20   $668.00