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	$225.65	13.131%	$255.2801	$255.28	$255.30	$255.30
Purchase #2	$108.93	3.177%	$112.3907	$112.39	$112.40	$112.40
Purchase #3	$229.98	12.372%	$258.4331	$258.43	$258.45	$258.40
Purchase #4	$93.67	9.141%	$102.2324	$102.23	$102.25	$102.20
Purchase #5	$76.53	4.501%	$79.9746	$79.97	$79.95	$80.00
Purchase #6	$69.54	13.244%	$78.7499	$78.75	$78.75	$78.70
Purchase #7	$73.92	11.711%	$82.5768	$82.58	$82.60	$82.60
7 purchase totals =	$878.22		$969.6376	$969.63	$969.70	$969.60