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	$88.39	13.379%	$100.2157	$100.22	$100.20	$100.20
Purchase #2	$123.69	8.405%	$134.0861	$134.09	$134.10	$134.10
Purchase #3	$24.26	13.262%	$27.4774	$27.48	$27.50	$27.50
Purchase #4	$149.35	12.683%	$168.2921	$168.29	$168.30	$168.30
Purchase #5	$44.31	11.221%	$49.282	$49.28	$49.30	$49.30
Purchase #6	$88.32	7.708%	$95.1277	$95.13	$95.15	$95.10
Purchase #7	$162.59	6.103%	$172.5129	$172.51	$172.50	$172.50
7 purchase totals =	$680.91		$746.9939	$747.00	$747.05	$747.00