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	$159.80	6.647%	$170.4219	$170.42	$170.40	$170.40
Purchase #2	$217.57	7.136%	$233.0958	$233.10	$233.10	$233.10
Purchase #3	$90.89	13.286%	$102.9656	$102.97	$102.95	$103.00
Purchase #4	$185.94	7.756%	$200.3615	$200.36	$200.35	$200.40
Purchase #5	$136.50	11.729%	$152.5101	$152.51	$152.50	$152.50
Purchase #6	$96.95	3.660%	$100.4984	$100.50	$100.50	$100.50
Purchase #7	$23.28	13.430%	$26.4065	$26.41	$26.40	$26.40
7 purchase totals =	$910.93		$986.2598	$986.27	$986.20	$986.30