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	$177.69	12.665%	$200.1944	$200.19	$200.20	$200.20
Purchase #2	$64.51	13.748%	$73.3788	$73.38	$73.40	$73.40
Purchase #3	$139.31	8.525%	$151.1862	$151.19	$151.20	$151.20
Purchase #4	$74.31	5.170%	$78.1518	$78.15	$78.15	$78.20
Purchase #5	$128.26	10.260%	$141.4195	$141.42	$141.40	$141.40
Purchase #6	$59.43	4.821%	$62.2951	$62.30	$62.30	$62.30
Purchase #7	$175.35	8.717%	$190.6353	$190.64	$190.65	$190.60
7 purchase totals =	$818.86		$897.2611	$897.27	$897.30	$897.30