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	$178.72	3.164%	$184.3747	$184.37	$184.35	$184.40
Purchase #2	$30.39	13.390%	$34.4592	$34.46	$34.45	$34.50
Purchase #3	$221.54	5.217%	$233.0977	$233.10	$233.10	$233.10
Purchase #4	$40.52	4.717%	$42.4313	$42.43	$42.45	$42.40
Purchase #5	$201.61	9.846%	$221.4605	$221.46	$221.45	$221.50
Purchase #6	$250.56	13.488%	$284.3555	$284.36	$284.35	$284.40
Purchase #7	$71.26	8.603%	$77.3905	$77.39	$77.40	$77.40
7 purchase totals =	$994.60		$1,077.5694	$1,077.57	$1,077.55	$1,077.70