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	$203.65	13.637%	$231.4218	$231.42	$231.40	$231.40
Purchase #2	$48.33	12.803%	$54.5177	$54.52	$54.50	$54.50
Purchase #3	$208.46	7.125%	$223.3128	$223.31	$223.30	$223.30
Purchase #4	$115.52	8.559%	$125.4074	$125.41	$125.40	$125.40
Purchase #5	$86.91	3.342%	$89.8145	$89.81	$89.80	$89.80
Purchase #6	$193.78	10.857%	$214.8187	$214.82	$214.80	$214.80
Purchase #7	$244.57	12.474%	$275.0777	$275.08	$275.10	$275.10
7 purchase totals =	$1,101.22		$1,214.3706	$1,214.37	$1,214.30	$1,214.30