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	$180.87	10.499%	$199.8595	$199.86	$199.85	$199.90
Purchase #2	$70.95	11.166%	$78.8723	$78.87	$78.85	$78.90
Purchase #3	$245.41	13.769%	$279.2005	$279.20	$279.20	$279.20
Purchase #4	$103.41	7.357%	$111.0179	$111.02	$111.00	$111.00
Purchase #5	$209.43	6.209%	$222.4335	$222.43	$222.45	$222.40
Purchase #6	$215.76	13.441%	$244.7603	$244.76	$244.75	$244.80
Purchase #7	$112.27	10.274%	$123.8046	$123.80	$123.80	$123.80
7 purchase totals =	$1,138.10		$1,259.9486	$1,259.94	$1,259.90	$1,260.00