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 $79.38   8.338%   $85.9987   $86.00   $86.00   $86.00  
  Purchase #2 $116.61   8.874%   $126.958   $126.96   $126.95   $127.00  
  Purchase #3 $33.27   5.267%   $35.0223   $35.02   $35.00   $35.00  
  Purchase #4 $98.87   5.307%   $104.117   $104.12   $104.10   $104.10  
  Purchase #5 $169.84   3.526%   $175.8286   $175.83   $175.85   $175.80  
  Purchase #6 $164.85   12.185%   $184.937   $184.94   $184.95   $184.90  
  Purchase #7 $199.94   5.403%   $210.7428   $210.74   $210.75   $210.70  
  7 purchase totals = $862.76       $923.6044   $923.61   $923.60   $923.50