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	$155.67	11.252%	$173.186	$173.19	$173.20	$173.20
Purchase #2	$50.66	4.191%	$52.7832	$52.78	$52.80	$52.80
Purchase #3	$82.36	9.677%	$90.33	$90.33	$90.35	$90.30
Purchase #4	$19.56	4.808%	$20.5004	$20.50	$20.50	$20.50
Purchase #5	$29.48	11.170%	$32.7729	$32.77	$32.75	$32.80
Purchase #6	$83.90	5.516%	$88.5279	$88.53	$88.55	$88.50
Purchase #7	$50.43	5.720%	$53.3146	$53.31	$53.30	$53.30
7 purchase totals =	$472.06		$511.4150	$511.41	$511.45	$511.40