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	$176.41	6.863%	$188.517	$188.52	$188.50	$188.50
Purchase #2	$170.52	5.591%	$180.0538	$180.05	$180.05	$180.10
Purchase #3	$197.85	10.396%	$218.4185	$218.42	$218.40	$218.40
Purchase #4	$65.30	13.249%	$73.9516	$73.95	$73.95	$74.00
Purchase #5	$74.76	10.372%	$82.5141	$82.51	$82.50	$82.50
Purchase #6	$132.88	4.784%	$139.237	$139.24	$139.25	$139.20
Purchase #7	$187.28	5.798%	$198.1385	$198.14	$198.15	$198.10
7 purchase totals =	$1,005.00		$1,080.8305	$1,080.83	$1,080.80	$1,080.80