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	$59.59	12.213%	$66.8677	$66.87	$66.85	$66.90
Purchase #2	$198.55	4.617%	$207.7171	$207.72	$207.70	$207.70
Purchase #3	$147.65	7.778%	$159.1342	$159.13	$159.15	$159.10
Purchase #4	$149.52	8.420%	$162.1096	$162.11	$162.10	$162.10
Purchase #5	$151.77	6.281%	$161.3027	$161.30	$161.30	$161.30
Purchase #6	$181.52	9.579%	$198.9078	$198.91	$198.90	$198.90
Purchase #7	$127.95	12.748%	$144.2611	$144.26	$144.25	$144.30
7 purchase totals =	$1,016.55		$1,100.3002	$1,100.30	$1,100.25	$1,100.30