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	$40.66	12.845%	$45.8828	$45.88	$45.90	$45.90
Purchase #2	$173.76	9.749%	$190.6999	$190.70	$190.70	$190.70
Purchase #3	$128.95	10.579%	$142.5916	$142.59	$142.60	$142.60
Purchase #4	$146.68	12.570%	$165.1177	$165.12	$165.10	$165.10
Purchase #5	$226.41	5.290%	$238.3871	$238.39	$238.40	$238.40
Purchase #6	$121.30	11.578%	$135.3441	$135.34	$135.35	$135.30
Purchase #7	$230.51	3.371%	$238.2805	$238.28	$238.30	$238.30
7 purchase totals =	$1,068.27		$1,156.3037	$1,156.30	$1,156.35	$1,156.30