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	$115.80	11.873%	$129.5489	$129.55	$129.55	$129.50
Purchase #2	$233.92	4.295%	$243.9669	$243.97	$243.95	$244.00
Purchase #3	$117.86	4.731%	$123.436	$123.44	$123.45	$123.40
Purchase #4	$109.56	5.407%	$115.4839	$115.48	$115.50	$115.50
Purchase #5	$11.39	4.753%	$11.9314	$11.93	$11.95	$11.90
Purchase #6	$158.56	9.422%	$173.4995	$173.50	$173.50	$173.50
Purchase #7	$172.28	4.701%	$180.3789	$180.38	$180.40	$180.40
7 purchase totals =	$919.37		$978.2455	$978.25	$978.30	$978.20