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 $201.76   6.247%   $214.3639   $214.36   $214.35   $214.40  
  Purchase #2 $86.88   4.537%   $90.8217   $90.82   $90.80   $90.80  
  Purchase #3 $63.59   8.331%   $68.8877   $68.89   $68.90   $68.90  
  Purchase #4 $72.54   5.409%   $76.4637   $76.46   $76.45   $76.50  
  Purchase #5 $57.68   13.207%   $65.2978   $65.30   $65.30   $65.30  
  Purchase #6 $53.50   8.429%   $58.0095   $58.01   $58.00   $58.00  
  Purchase #7 $47.27   12.559%   $53.2066   $53.21   $53.20   $53.20  
  7 purchase totals = $583.22       $627.0509   $627.05   $627.00   $627.10