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	$19.67	7.381%	$21.1218	$21.12	$21.10	$21.10
Purchase #2	$31.82	5.203%	$33.4756	$33.48	$33.50	$33.50
Purchase #3	$167.64	10.160%	$184.6722	$184.67	$184.65	$184.70
Purchase #4	$228.76	5.658%	$241.7032	$241.70	$241.70	$241.70
Purchase #5	$99.79	11.613%	$111.3786	$111.38	$111.40	$111.40
Purchase #6	$117.30	8.656%	$127.4535	$127.45	$127.45	$127.50
Purchase #7	$48.71	9.359%	$53.2688	$53.27	$53.25	$53.30
7 purchase totals =	$713.69		$773.0737	$773.07	$773.05	$773.20