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	$143.69	10.740%	$159.1223	$159.12	$159.10	$159.10
Purchase #2	$114.66	6.822%	$122.4821	$122.48	$122.50	$122.50
Purchase #3	$43.36	9.551%	$47.5013	$47.50	$47.50	$47.50
Purchase #4	$105.42	5.596%	$111.3193	$111.32	$111.30	$111.30
Purchase #5	$138.27	4.471%	$144.4521	$144.45	$144.45	$144.50
Purchase #6	$45.98	8.605%	$49.9366	$49.94	$49.95	$49.90
Purchase #7	$130.70	11.472%	$145.6939	$145.69	$145.70	$145.70
7 purchase totals =	$722.08		$780.5076	$780.50	$780.50	$780.50