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	$247.25	3.748%	$256.5169	$256.52	$256.50	$256.50
Purchase #2	$38.38	10.575%	$42.4387	$42.44	$42.45	$42.40
Purchase #3	$42.82	7.335%	$45.9608	$45.96	$45.95	$46.00
Purchase #4	$249.46	4.395%	$260.4238	$260.42	$260.40	$260.40
Purchase #5	$188.34	11.647%	$210.276	$210.28	$210.30	$210.30
Purchase #6	$78.37	12.425%	$88.1075	$88.11	$88.10	$88.10
Purchase #7	$227.78	3.553%	$235.873	$235.87	$235.85	$235.90
7 purchase totals =	$1,072.40		$1,139.5967	$1,139.60	$1,139.55	$1,139.60