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 $59.52   5.827%   $62.9882   $62.99   $63.00   $63.00  
  Purchase #2 $238.26   11.841%   $266.4724   $266.47   $266.45   $266.50  
  Purchase #3 $159.50   8.588%   $173.1979   $173.20   $173.20   $173.20  
  Purchase #4 $58.29   12.698%   $65.6917   $65.69   $65.70   $65.70  
  Purchase #5 $135.72   6.509%   $144.554   $144.55   $144.55   $144.60  
  Purchase #6 $86.68   10.856%   $96.09   $96.09   $96.10   $96.10  
  Purchase #7 $7.73   6.652%   $8.2442   $8.24   $8.25   $8.20  
  7 purchase totals = $745.70       $817.2384   $817.23   $817.25   $817.30