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	$228.41	12.308%	$256.5227	$256.52	$256.50	$256.50
Purchase #2	$75.32	9.548%	$82.5116	$82.51	$82.50	$82.50
Purchase #3	$113.33	9.770%	$124.4023	$124.40	$124.40	$124.40
Purchase #4	$193.73	10.441%	$213.9573	$213.96	$213.95	$214.00
Purchase #5	$165.61	7.581%	$178.1649	$178.16	$178.15	$178.20
Purchase #6	$129.78	12.552%	$146.07	$146.07	$146.05	$146.10
Purchase #7	$72.67	5.839%	$76.9132	$76.91	$76.90	$76.90
7 purchase totals =	$978.85		$1,078.5420	$1,078.53	$1,078.45	$1,078.60