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	$234.65	3.268%	$242.3184	$242.32	$242.30	$242.30
Purchase #2	$35.68	5.865%	$37.7726	$37.77	$37.75	$37.80
Purchase #3	$161.80	13.281%	$183.2887	$183.29	$183.30	$183.30
Purchase #4	$19.32	4.254%	$20.1419	$20.14	$20.15	$20.10
Purchase #5	$99.51	10.346%	$109.8053	$109.81	$109.80	$109.80
Purchase #6	$209.86	13.653%	$238.5122	$238.51	$238.50	$238.50
Purchase #7	$149.40	3.653%	$154.8576	$154.86	$154.85	$154.90
7 purchase totals =	$910.22		$986.6967	$986.70	$986.65	$986.70