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	$92.42	8.434%	$100.2147	$100.21	$100.20	$100.20
Purchase #2	$133.65	11.305%	$148.7591	$148.76	$148.75	$148.80
Purchase #3	$116.50	13.683%	$132.4407	$132.44	$132.45	$132.40
Purchase #4	$87.97	3.131%	$90.7243	$90.72	$90.70	$90.70
Purchase #5	$51.95	9.573%	$56.9232	$56.92	$56.90	$56.90
Purchase #6	$90.98	3.494%	$94.1588	$94.16	$94.15	$94.20
Purchase #7	$171.83	3.830%	$178.4111	$178.41	$178.40	$178.40
7 purchase totals =	$745.30		$801.6319	$801.62	$801.55	$801.60