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	$155.27	8.665%	$168.7241	$168.72	$168.70	$168.70
Purchase #2	$116.55	8.798%	$126.8041	$126.80	$126.80	$126.80
Purchase #3	$42.48	10.123%	$46.7803	$46.78	$46.80	$46.80
Purchase #4	$49.52	4.137%	$51.5686	$51.57	$51.55	$51.60
Purchase #5	$133.66	7.368%	$143.5081	$143.51	$143.50	$143.50
Purchase #6	$154.69	6.667%	$165.0032	$165.00	$165.00	$165.00
Purchase #7	$89.35	3.215%	$92.2226	$92.22	$92.20	$92.20
7 purchase totals =	$741.52		$794.6110	$794.60	$794.55	$794.60