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 $61.83   6.692%   $65.9677   $65.97   $65.95   $66.00  
  Purchase #2 $147.84   11.785%   $165.2629   $165.26   $165.25   $165.30  
  Purchase #3 $30.76   11.281%   $34.23   $34.23   $34.25   $34.20  
  Purchase #4 $233.27   6.421%   $248.2483   $248.25   $248.25   $248.20  
  Purchase #5 $89.49   7.800%   $96.4702   $96.47   $96.45   $96.50  
  Purchase #6 $155.92   8.789%   $169.6238   $169.62   $169.60   $169.60  
  Purchase #7 $168.88   9.124%   $184.2886   $184.29   $184.30   $184.30  
  7 purchase totals = $887.99       $964.0915   $964.09   $964.05   $964.10