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	$155.92	5.772%	$164.9197	$164.92	$164.90	$164.90
Purchase #2	$20.28	10.109%	$22.3301	$22.33	$22.35	$22.30
Purchase #3	$25.60	11.323%	$28.4987	$28.50	$28.50	$28.50
Purchase #4	$58.79	5.572%	$62.0658	$62.07	$62.05	$62.10
Purchase #5	$100.98	10.834%	$111.9202	$111.92	$111.90	$111.90
Purchase #6	$163.93	4.259%	$170.9118	$170.91	$170.90	$170.90
Purchase #7	$145.70	8.646%	$158.2972	$158.30	$158.30	$158.30
7 purchase totals =	$671.20		$718.9435	$718.95	$718.90	$718.90