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	$105.78	5.492%	$111.5894	$111.59	$111.60	$111.60
Purchase #2	$79.68	3.868%	$82.762	$82.76	$82.75	$82.80
Purchase #3	$58.38	13.352%	$66.1749	$66.17	$66.15	$66.20
Purchase #4	$81.97	13.340%	$92.9048	$92.90	$92.90	$92.90
Purchase #5	$153.94	4.775%	$161.2906	$161.29	$161.30	$161.30
Purchase #6	$220.77	9.848%	$242.5114	$242.51	$242.50	$242.50
Purchase #7	$162.46	11.841%	$181.6969	$181.70	$181.70	$181.70
7 purchase totals =	$862.98		$938.9300	$938.92	$938.90	$939.00