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	$245.25	6.174%	$260.3917	$260.39	$260.40	$260.40
Purchase #2	$137.43	9.732%	$150.8047	$150.80	$150.80	$150.80
Purchase #3	$48.72	11.606%	$54.3744	$54.37	$54.35	$54.40
Purchase #4	$120.68	5.557%	$127.3862	$127.39	$127.40	$127.40
Purchase #5	$198.30	11.784%	$221.6677	$221.67	$221.65	$221.70
Purchase #6	$156.41	7.335%	$167.8827	$167.88	$167.90	$167.90
Purchase #7	$105.29	10.863%	$116.7277	$116.73	$116.75	$116.70
7 purchase totals =	$1,012.08		$1,099.2351	$1,099.23	$1,099.25	$1,099.30