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	$15.36	5.550%	$16.2125	$16.21	$16.20	$16.20
Purchase #2	$144.72	12.535%	$162.8607	$162.86	$162.85	$162.90
Purchase #3	$91.75	8.604%	$99.6442	$99.64	$99.65	$99.60
Purchase #4	$88.30	4.820%	$92.5561	$92.56	$92.55	$92.60
Purchase #5	$104.42	7.107%	$111.8411	$111.84	$111.85	$111.80
Purchase #6	$44.64	13.252%	$50.5557	$50.56	$50.55	$50.60
Purchase #7	$51.94	6.478%	$55.3047	$55.30	$55.30	$55.30
7 purchase totals =	$541.13		$588.9750	$588.97	$588.95	$589.00