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	$154.77	12.220%	$173.6829	$173.68	$173.70	$173.70
Purchase #2	$38.43	11.239%	$42.7491	$42.75	$42.75	$42.70
Purchase #3	$144.27	6.606%	$153.8005	$153.80	$153.80	$153.80
Purchase #4	$82.92	5.643%	$87.5992	$87.60	$87.60	$87.60
Purchase #5	$168.74	4.465%	$176.2742	$176.27	$176.25	$176.30
Purchase #6	$30.92	9.559%	$33.8756	$33.88	$33.90	$33.90
Purchase #7	$30.30	8.578%	$32.8991	$32.90	$32.90	$32.90
7 purchase totals =	$650.35		$700.8806	$700.88	$700.90	$700.90