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	$109.88	13.144%	$124.3226	$124.32	$124.30	$124.30
Purchase #2	$224.90	3.671%	$233.1561	$233.16	$233.15	$233.20
Purchase #3	$81.52	10.203%	$89.8375	$89.84	$89.85	$89.80
Purchase #4	$104.47	6.203%	$110.9503	$110.95	$110.95	$111.00
Purchase #5	$149.45	5.870%	$158.2227	$158.22	$158.20	$158.20
Purchase #6	$133.75	8.177%	$144.6867	$144.69	$144.70	$144.70
Purchase #7	$151.87	13.787%	$172.8083	$172.81	$172.80	$172.80
7 purchase totals =	$955.84		$1,033.9842	$1,033.99	$1,033.95	$1,034.00