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	$31.27	12.246%	$35.0993	$35.10	$35.10	$35.10
Purchase #2	$105.61	5.536%	$111.4566	$111.46	$111.45	$111.50
Purchase #3	$188.58	7.184%	$202.1276	$202.13	$202.15	$202.10
Purchase #4	$70.44	10.593%	$77.9017	$77.90	$77.90	$77.90
Purchase #5	$147.54	10.110%	$162.4563	$162.46	$162.45	$162.50
Purchase #6	$53.78	3.310%	$55.5601	$55.56	$55.55	$55.60
Purchase #7	$244.49	8.248%	$264.6555	$264.66	$264.65	$264.70
7 purchase totals =	$841.71		$909.2571	$909.27	$909.25	$909.40