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 $237.96   12.246%   $267.1006   $267.10   $267.10   $267.10  
  Purchase #2 $109.95   5.486%   $115.9819   $115.98   $116.00   $116.00  
  Purchase #3 $53.36   13.673%   $60.6559   $60.66   $60.65   $60.70  
  Purchase #4 $213.76   3.643%   $221.5473   $221.55   $221.55   $221.50  
  Purchase #5 $188.59   7.512%   $202.7569   $202.76   $202.75   $202.80  
  Purchase #6 $90.57   8.164%   $97.9641   $97.96   $97.95   $98.00  
  Purchase #7 $57.32   10.350%   $63.2526   $63.25   $63.25   $63.30  
  7 purchase totals = $951.51       $1,029.2593   $1,029.26   $1,029.25   $1,029.40