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	$123.97	3.816%	$128.7007	$128.70	$128.70	$128.70
Purchase #2	$158.74	4.395%	$165.7166	$165.72	$165.70	$165.70
Purchase #3	$123.25	3.162%	$127.1472	$127.15	$127.15	$127.10
Purchase #4	$197.67	8.833%	$215.1302	$215.13	$215.15	$215.10
Purchase #5	$45.54	6.727%	$48.6035	$48.60	$48.60	$48.60
Purchase #6	$73.85	7.395%	$79.3112	$79.31	$79.30	$79.30
Purchase #7	$90.64	9.307%	$99.0759	$99.08	$99.10	$99.10
7 purchase totals =	$813.66		$863.6853	$863.69	$863.70	$863.60