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	$48.78	13.102%	$55.1712	$55.17	$55.15	$55.20
Purchase #2	$131.46	7.627%	$141.4865	$141.49	$141.50	$141.50
Purchase #3	$173.51	7.687%	$186.8477	$186.85	$186.85	$186.80
Purchase #4	$44.78	4.162%	$46.6437	$46.64	$46.65	$46.60
Purchase #5	$54.60	4.561%	$57.0903	$57.09	$57.10	$57.10
Purchase #6	$95.89	9.158%	$104.6716	$104.67	$104.65	$104.70
Purchase #7	$17.82	13.659%	$20.254	$20.25	$20.25	$20.30
7 purchase totals =	$566.84		$612.1650	$612.16	$612.15	$612.20