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	$47.47	4.186%	$49.4571	$49.46	$49.45	$49.50
Purchase #2	$172.75	13.505%	$196.0799	$196.08	$196.10	$196.10
Purchase #3	$73.72	11.821%	$82.4344	$82.43	$82.45	$82.40
Purchase #4	$79.36	5.657%	$83.8494	$83.85	$83.85	$83.80
Purchase #5	$54.54	10.204%	$60.1053	$60.11	$60.10	$60.10
Purchase #6	$70.86	5.194%	$74.5405	$74.54	$74.55	$74.50
Purchase #7	$67.45	11.761%	$75.3828	$75.38	$75.40	$75.40
7 purchase totals =	$566.15		$621.8494	$621.85	$621.90	$621.80