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	$50.56	11.543%	$56.3961	$56.40	$56.40	$56.40
Purchase #2	$233.32	7.207%	$250.1354	$250.14	$250.15	$250.10
Purchase #3	$78.59	3.845%	$81.6118	$81.61	$81.60	$81.60
Purchase #4	$19.76	13.437%	$22.4152	$22.42	$22.40	$22.40
Purchase #5	$109.52	9.428%	$119.8455	$119.85	$119.85	$119.80
Purchase #6	$189.55	8.409%	$205.4893	$205.49	$205.50	$205.50
Purchase #7	$45.91	5.548%	$48.4571	$48.46	$48.45	$48.50
7 purchase totals =	$727.21		$784.3504	$784.37	$784.35	$784.30