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	$25.64	6.442%	$27.2917	$27.29	$27.30	$27.30
Purchase #2	$216.72	4.385%	$226.2232	$226.22	$226.20	$226.20
Purchase #3	$130.65	10.280%	$144.0808	$144.08	$144.10	$144.10
Purchase #4	$87.97	8.660%	$95.5882	$95.59	$95.60	$95.60
Purchase #5	$30.85	5.640%	$32.5899	$32.59	$32.60	$32.60
Purchase #6	$54.38	9.759%	$59.6869	$59.69	$59.70	$59.70
Purchase #7	$141.37	12.221%	$158.6468	$158.65	$158.65	$158.60
7 purchase totals =	$687.58		$744.1075	$744.11	$744.15	$744.10