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	$239.52	12.345%	$269.0887	$269.09	$269.10	$269.10
Purchase #2	$241.45	12.573%	$271.8075	$271.81	$271.80	$271.80
Purchase #3	$133.59	10.581%	$147.7252	$147.73	$147.75	$147.70
Purchase #4	$135.25	11.699%	$151.0729	$151.07	$151.05	$151.10
Purchase #5	$51.90	4.621%	$54.2983	$54.30	$54.30	$54.30
Purchase #6	$243.87	7.505%	$262.1724	$262.17	$262.15	$262.20
Purchase #7	$59.64	9.247%	$65.1549	$65.15	$65.15	$65.20
7 purchase totals =	$1,105.22		$1,221.3199	$1,221.32	$1,221.30	$1,221.40