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	$90.31	9.661%	$99.0348	$99.03	$99.05	$99.00
Purchase #2	$223.54	9.519%	$244.8188	$244.82	$244.80	$244.80
Purchase #3	$238.90	4.143%	$248.7976	$248.80	$248.80	$248.80
Purchase #4	$198.95	11.707%	$222.2411	$222.24	$222.25	$222.20
Purchase #5	$135.90	11.196%	$151.1154	$151.12	$151.10	$151.10
Purchase #6	$151.71	6.295%	$161.2601	$161.26	$161.25	$161.30
Purchase #7	$128.25	12.176%	$143.8657	$143.87	$143.85	$143.90
7 purchase totals =	$1,167.56		$1,271.1335	$1,271.14	$1,271.10	$1,271.10