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 $41.40   12.258%   $46.4748   $46.47   $46.45   $46.50  
  Purchase #2 $246.49   7.269%   $264.4074   $264.41   $264.40   $264.40  
  Purchase #3 $103.44   11.830%   $115.677   $115.68   $115.70   $115.70  
  Purchase #4 $65.75   7.842%   $70.9061   $70.91   $70.90   $70.90  
  Purchase #5 $192.53   8.231%   $208.3771   $208.38   $208.40   $208.40  
  Purchase #6 $66.44   10.792%   $73.6102   $73.61   $73.60   $73.60  
  Purchase #7 $190.43   13.319%   $215.7934   $215.79   $215.80   $215.80  
  7 purchase totals = $906.48       $995.2460   $995.25   $995.25   $995.30