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	$90.29	10.828%	$100.0666	$100.07	$100.05	$100.10
Purchase #2	$159.74	4.721%	$167.2813	$167.28	$167.30	$167.30
Purchase #3	$221.89	13.672%	$252.2268	$252.23	$252.25	$252.20
Purchase #4	$92.97	10.609%	$102.8332	$102.83	$102.85	$102.80
Purchase #5	$101.57	7.760%	$109.4518	$109.45	$109.45	$109.50
Purchase #6	$164.95	12.318%	$185.2685	$185.27	$185.25	$185.30
Purchase #7	$188.96	11.286%	$210.286	$210.29	$210.30	$210.30
7 purchase totals =	$1,020.37		$1,127.4142	$1,127.42	$1,127.45	$1,127.50