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	$115.74	9.295%	$126.498	$126.50	$126.50	$126.50
Purchase #2	$168.28	4.235%	$175.4067	$175.41	$175.40	$175.40
Purchase #3	$89.42	7.169%	$95.8305	$95.83	$95.85	$95.80
Purchase #4	$114.49	7.787%	$123.4053	$123.41	$123.40	$123.40
Purchase #5	$205.52	11.606%	$229.3727	$229.37	$229.35	$229.40
Purchase #6	$130.60	6.457%	$139.0328	$139.03	$139.05	$139.00
Purchase #7	$59.51	8.408%	$64.5136	$64.51	$64.50	$64.50
7 purchase totals =	$883.56		$954.0596	$954.06	$954.05	$954.00