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	$28.55	10.194%	$31.4604	$31.46	$31.45	$31.50
Purchase #2	$35.85	3.564%	$37.1277	$37.13	$37.15	$37.10
Purchase #3	$78.26	9.723%	$85.8692	$85.87	$85.85	$85.90
Purchase #4	$36.91	12.579%	$41.5529	$41.55	$41.55	$41.60
Purchase #5	$54.90	9.777%	$60.2676	$60.27	$60.25	$60.30
Purchase #6	$60.76	9.506%	$66.5358	$66.54	$66.55	$66.50
Purchase #7	$214.84	7.353%	$230.6372	$230.64	$230.65	$230.60
7 purchase totals =	$510.07		$553.4508	$553.46	$553.45	$553.50