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	$230.91	10.613%	$255.4165	$255.42	$255.40	$255.40
Purchase #2	$225.34	10.722%	$249.501	$249.50	$249.50	$249.50
Purchase #3	$193.35	13.437%	$219.3304	$219.33	$219.35	$219.30
Purchase #4	$146.68	4.271%	$152.9447	$152.94	$152.95	$152.90
Purchase #5	$155.47	8.142%	$168.1284	$168.13	$168.15	$168.10
Purchase #6	$170.48	11.800%	$190.5966	$190.60	$190.60	$190.60
Purchase #7	$158.57	13.750%	$180.3734	$180.37	$180.35	$180.40
7 purchase totals =	$1,280.80		$1,416.2910	$1,416.29	$1,416.30	$1,416.20