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	$56.70	3.343%	$58.5955	$58.60	$58.60	$58.60
Purchase #2	$101.63	9.663%	$111.4505	$111.45	$111.45	$111.50
Purchase #3	$153.93	12.659%	$173.416	$173.42	$173.40	$173.40
Purchase #4	$249.52	4.608%	$261.0179	$261.02	$261.00	$261.00
Purchase #5	$125.45	6.851%	$134.0446	$134.04	$134.05	$134.00
Purchase #6	$176.50	7.748%	$190.1752	$190.18	$190.20	$190.20
Purchase #7	$145.99	3.838%	$151.5931	$151.59	$151.60	$151.60
7 purchase totals =	$1,009.72		$1,080.2928	$1,080.30	$1,080.30	$1,080.30