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 $59.77   13.836%   $68.0398   $68.04   $68.05   $68.00  
  Purchase #2 $12.77   9.431%   $13.9743   $13.97   $13.95   $14.00  
  Purchase #3 $63.82   10.423%   $70.472   $70.47   $70.45   $70.50  
  Purchase #4 $83.83   7.745%   $90.3226   $90.32   $90.30   $90.30  
  Purchase #5 $118.97   6.725%   $126.9707   $126.97   $126.95   $127.00  
  Purchase #6 $188.90   10.337%   $208.4266   $208.43   $208.45   $208.40  
  Purchase #7 $115.59   7.432%   $124.1806   $124.18   $124.20   $124.20  
  7 purchase totals = $643.65       $702.3866   $702.38   $702.35   $702.40