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	$38.42	4.349%	$40.0909	$40.09	$40.10	$40.10
Purchase #2	$111.82	10.555%	$123.6226	$123.62	$123.60	$123.60
Purchase #3	$70.95	5.462%	$74.8253	$74.83	$74.85	$74.80
Purchase #4	$129.39	11.415%	$144.1599	$144.16	$144.15	$144.20
Purchase #5	$139.30	5.613%	$147.1189	$147.12	$147.10	$147.10
Purchase #6	$190.93	11.352%	$212.6044	$212.60	$212.60	$212.60
Purchase #7	$229.91	6.109%	$243.9552	$243.96	$243.95	$244.00
7 purchase totals =	$910.72		$986.3772	$986.38	$986.35	$986.40