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 $183.29   13.468%   $207.9755   $207.98   $208.00   $208.00  
  Purchase #2 $197.57   8.134%   $213.6403   $213.64   $213.65   $213.60  
  Purchase #3 $126.97   10.205%   $139.9273   $139.93   $139.95   $139.90  
  Purchase #4 $154.86   9.481%   $169.5423   $169.54   $169.55   $169.50  
  Purchase #5 $78.64   12.361%   $88.3607   $88.36   $88.35   $88.40  
  Purchase #6 $226.36   9.588%   $248.0634   $248.06   $248.05   $248.10  
  Purchase #7 $189.86   4.845%   $199.0587   $199.06   $199.05   $199.10  
  7 purchase totals = $1,157.55       $1,266.5682   $1,266.57   $1,266.60   $1,266.60