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	$108.93	13.760%	$123.9188	$123.92	$123.90	$123.90
Purchase #2	$39.67	13.515%	$45.0314	$45.03	$45.05	$45.00
Purchase #3	$165.66	7.515%	$178.1093	$178.11	$178.10	$178.10
Purchase #4	$64.54	9.645%	$70.7649	$70.76	$70.75	$70.80
Purchase #5	$118.54	7.520%	$127.4542	$127.45	$127.45	$127.50
Purchase #6	$176.31	5.326%	$185.7003	$185.70	$185.70	$185.70
Purchase #7	$228.50	3.598%	$236.7214	$236.72	$236.70	$236.70
7 purchase totals =	$902.15		$967.7003	$967.69	$967.65	$967.70