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 $114.83   10.639%   $127.0468   $127.05   $127.05   $127.00  
  Purchase #2 $30.73   8.433%   $33.3215   $33.32   $33.30   $33.30  
  Purchase #3 $74.72   13.163%   $84.5554   $84.56   $84.55   $84.60  
  Purchase #4 $59.25   4.334%   $61.8179   $61.82   $61.80   $61.80  
  Purchase #5 $213.44   12.426%   $239.9621   $239.96   $239.95   $240.00  
  Purchase #6 $125.60   13.279%   $142.2784   $142.28   $142.30   $142.30  
  Purchase #7 $83.70   12.622%   $94.2646   $94.26   $94.25   $94.30  
  7 purchase totals = $702.27       $783.2467   $783.25   $783.20   $783.30