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	$97.81	11.585%	$109.1413	$109.14	$109.15	$109.10
Purchase #2	$159.59	7.368%	$171.3486	$171.35	$171.35	$171.30
Purchase #3	$168.89	5.764%	$178.6248	$178.62	$178.60	$178.60
Purchase #4	$70.49	4.777%	$73.8573	$73.86	$73.85	$73.90
Purchase #5	$175.35	10.318%	$193.4426	$193.44	$193.45	$193.40
Purchase #6	$71.35	10.655%	$78.9523	$78.95	$78.95	$79.00
Purchase #7	$101.71	9.277%	$111.1456	$111.15	$111.15	$111.10
7 purchase totals =	$845.19		$916.5125	$916.51	$916.50	$916.40