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	$49.74	3.784%	$51.6222	$51.62	$51.60	$51.60
Purchase #2	$56.76	4.176%	$59.1303	$59.13	$59.15	$59.10
Purchase #3	$112.66	6.720%	$120.2308	$120.23	$120.25	$120.20
Purchase #4	$163.72	13.522%	$185.8582	$185.86	$185.85	$185.90
Purchase #5	$91.81	8.332%	$99.4596	$99.46	$99.45	$99.50
Purchase #6	$137.37	4.828%	$144.0022	$144.00	$144.00	$144.00
Purchase #7	$202.53	4.194%	$211.0241	$211.02	$211.00	$211.00
7 purchase totals =	$814.59		$871.3274	$871.32	$871.30	$871.30