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	$122.76	4.162%	$127.8693	$127.87	$127.85	$127.90
Purchase #2	$39.27	11.382%	$43.7397	$43.74	$43.75	$43.70
Purchase #3	$110.29	11.561%	$123.0406	$123.04	$123.05	$123.00
Purchase #4	$10.90	7.283%	$11.6938	$11.69	$11.70	$11.70
Purchase #5	$242.28	13.824%	$275.7728	$275.77	$275.75	$275.80
Purchase #6	$159.25	10.268%	$175.6018	$175.60	$175.60	$175.60
Purchase #7	$193.48	9.802%	$212.4449	$212.44	$212.45	$212.40
7 purchase totals =	$878.23		$970.1629	$970.15	$970.15	$970.10