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	$50.25	13.485%	$57.0262	$57.03	$57.05	$57.00
Purchase #2	$247.89	5.693%	$262.0024	$262.00	$262.00	$262.00
Purchase #3	$140.90	12.730%	$158.8366	$158.84	$158.85	$158.80
Purchase #4	$240.51	4.338%	$250.9433	$250.94	$250.95	$250.90
Purchase #5	$239.40	6.640%	$255.2962	$255.30	$255.30	$255.30
Purchase #6	$46.92	8.290%	$50.8097	$50.81	$50.80	$50.80
Purchase #7	$170.25	7.180%	$182.474	$182.47	$182.45	$182.50
7 purchase totals =	$1,136.12		$1,217.3884	$1,217.39	$1,217.40	$1,217.30