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	$13.62	13.365%	$15.4403	$15.44	$15.45	$15.40
Purchase #2	$50.42	8.863%	$54.8887	$54.89	$54.90	$54.90
Purchase #3	$148.76	11.703%	$166.1694	$166.17	$166.15	$166.20
Purchase #4	$47.51	12.435%	$53.4179	$53.42	$53.40	$53.40
Purchase #5	$248.46	8.463%	$269.4872	$269.49	$269.50	$269.50
Purchase #6	$244.26	6.114%	$259.1941	$259.19	$259.20	$259.20
Purchase #7	$84.94	6.321%	$90.3091	$90.31	$90.30	$90.30
7 purchase totals =	$837.97		$908.9067	$908.91	$908.90	$908.90