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	$48.87	4.431%	$51.0354	$51.04	$51.05	$51.00
Purchase #2	$50.26	10.265%	$55.4192	$55.42	$55.40	$55.40
Purchase #3	$44.30	4.675%	$46.371	$46.37	$46.35	$46.40
Purchase #4	$82.51	3.702%	$85.5645	$85.56	$85.55	$85.60
Purchase #5	$85.68	4.603%	$89.6239	$89.62	$89.60	$89.60
Purchase #6	$70.93	4.707%	$74.2687	$74.27	$74.25	$74.30
Purchase #7	$219.78	8.704%	$238.9097	$238.91	$238.90	$238.90
7 purchase totals =	$602.33		$641.1924	$641.19	$641.10	$641.20