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	$38.44	7.686%	$41.3945	$41.39	$41.40	$41.40
Purchase #2	$112.66	13.388%	$127.7429	$127.74	$127.75	$127.70
Purchase #3	$220.80	4.585%	$230.9237	$230.92	$230.90	$230.90
Purchase #4	$149.52	12.742%	$168.5718	$168.57	$168.55	$168.60
Purchase #5	$49.51	12.460%	$55.6789	$55.68	$55.70	$55.70
Purchase #6	$61.85	4.609%	$64.7007	$64.70	$64.70	$64.70
Purchase #7	$75.64	13.145%	$85.5829	$85.58	$85.60	$85.60
7 purchase totals =	$708.42		$774.5954	$774.58	$774.60	$774.60