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	$88.61	13.779%	$100.8196	$100.82	$100.80	$100.80
Purchase #2	$105.73	5.718%	$111.7756	$111.78	$111.80	$111.80
Purchase #3	$200.25	12.441%	$225.1631	$225.16	$225.15	$225.20
Purchase #4	$146.56	10.149%	$161.4344	$161.43	$161.45	$161.40
Purchase #5	$118.45	5.424%	$124.8747	$124.87	$124.85	$124.90
Purchase #6	$36.46	7.233%	$39.0972	$39.10	$39.10	$39.10
Purchase #7	$139.84	8.263%	$151.395	$151.40	$151.40	$151.40
7 purchase totals =	$835.90		$914.5596	$914.56	$914.55	$914.60