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	$168.90	5.501%	$178.1912	$178.19	$178.20	$178.20
Purchase #2	$242.92	13.519%	$275.7604	$275.76	$275.75	$275.80
Purchase #3	$38.50	6.809%	$41.1215	$41.12	$41.10	$41.10
Purchase #4	$10.29	10.337%	$11.3537	$11.35	$11.35	$11.40
Purchase #5	$75.43	9.613%	$82.6811	$82.68	$82.70	$82.70
Purchase #6	$91.47	12.672%	$103.0611	$103.06	$103.05	$103.10
Purchase #7	$174.27	6.523%	$185.6376	$185.64	$185.65	$185.60
7 purchase totals =	$801.78		$877.8066	$877.80	$877.80	$877.90