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	$34.90	10.870%	$38.6936	$38.69	$38.70	$38.70
Purchase #2	$173.33	5.766%	$183.3242	$183.32	$183.30	$183.30
Purchase #3	$32.58	6.156%	$34.5856	$34.59	$34.60	$34.60
Purchase #4	$204.27	3.856%	$212.1467	$212.15	$212.15	$212.10
Purchase #5	$61.66	4.291%	$64.3058	$64.31	$64.30	$64.30
Purchase #6	$222.38	5.395%	$234.3774	$234.38	$234.40	$234.40
Purchase #7	$64.50	11.388%	$71.8453	$71.85	$71.85	$71.80
7 purchase totals =	$793.62		$839.2786	$839.29	$839.30	$839.20