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	$46.88	6.782%	$50.0594	$50.06	$50.05	$50.10
Purchase #2	$160.50	7.178%	$172.0207	$172.02	$172.00	$172.00
Purchase #3	$26.54	11.368%	$29.5571	$29.56	$29.55	$29.60
Purchase #4	$112.53	13.237%	$127.4256	$127.43	$127.45	$127.40
Purchase #5	$60.43	5.802%	$63.9361	$63.94	$63.95	$63.90
Purchase #6	$99.88	13.648%	$113.5116	$113.51	$113.50	$113.50
Purchase #7	$123.86	5.529%	$130.7082	$130.71	$130.70	$130.70
7 purchase totals =	$630.62		$687.2187	$687.23	$687.20	$687.20