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	$158.58	13.617%	$180.1738	$180.17	$180.15	$180.20
Purchase #2	$41.84	8.690%	$45.4759	$45.48	$45.50	$45.50
Purchase #3	$132.76	10.508%	$146.7104	$146.71	$146.70	$146.70
Purchase #4	$28.40	9.456%	$31.0855	$31.09	$31.10	$31.10
Purchase #5	$166.53	11.438%	$185.5777	$185.58	$185.60	$185.60
Purchase #6	$152.52	12.109%	$170.9886	$170.99	$171.00	$171.00
Purchase #7	$122.91	7.127%	$131.6698	$131.67	$131.65	$131.70
7 purchase totals =	$803.54		$891.6817	$891.69	$891.70	$891.80