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	$77.86	5.323%	$82.0045	$82.00	$82.00	$82.00
Purchase #2	$44.61	11.460%	$49.7223	$49.72	$49.70	$49.70
Purchase #3	$126.29	5.751%	$133.5529	$133.55	$133.55	$133.60
Purchase #4	$95.47	10.256%	$105.2614	$105.26	$105.25	$105.30
Purchase #5	$81.67	12.392%	$91.7905	$91.79	$91.80	$91.80
Purchase #6	$132.67	9.510%	$145.2869	$145.29	$145.30	$145.30
Purchase #7	$113.72	12.869%	$128.3546	$128.35	$128.35	$128.40
7 purchase totals =	$672.29		$735.9731	$735.96	$735.95	$736.10