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 $86.40   12.209%   $96.9486   $96.95   $96.95   $96.90  
  Purchase #2 $61.50   6.182%   $65.3019   $65.30   $65.30   $65.30  
  Purchase #3 $70.40   13.158%   $79.6632   $79.66   $79.65   $79.70  
  Purchase #4 $93.46   11.225%   $103.9509   $103.95   $103.95   $104.00  
  Purchase #5 $48.39   10.294%   $53.3713   $53.37   $53.35   $53.40  
  Purchase #6 $140.25   12.326%   $157.5372   $157.54   $157.55   $157.50  
  Purchase #7 $226.58   9.660%   $248.4676   $248.47   $248.45   $248.50  
  7 purchase totals = $726.98       $805.2407   $805.24   $805.20   $805.30