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	$143.40	8.279%	$155.2721	$155.27	$155.25	$155.30
Purchase #2	$6.31	6.772%	$6.7373	$6.74	$6.75	$6.70
Purchase #3	$27.66	6.406%	$29.4319	$29.43	$29.45	$29.40
Purchase #4	$152.35	13.525%	$172.9553	$172.96	$172.95	$173.00
Purchase #5	$63.87	12.457%	$71.8263	$71.83	$71.85	$71.80
Purchase #6	$105.56	11.595%	$117.7997	$117.80	$117.80	$117.80
Purchase #7	$108.38	3.251%	$111.9034	$111.90	$111.90	$111.90
7 purchase totals =	$607.53		$665.9260	$665.93	$665.95	$665.90