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	$50.60	11.370%	$56.3532	$56.35	$56.35	$56.40
Purchase #2	$189.25	13.828%	$215.4195	$215.42	$215.40	$215.40
Purchase #3	$178.49	9.421%	$195.3055	$195.31	$195.30	$195.30
Purchase #4	$133.61	7.778%	$144.0022	$144.00	$144.00	$144.00
Purchase #5	$114.52	11.571%	$127.7711	$127.77	$127.75	$127.80
Purchase #6	$34.63	4.107%	$36.0523	$36.05	$36.05	$36.10
Purchase #7	$39.30	3.251%	$40.5776	$40.58	$40.60	$40.60
7 purchase totals =	$740.40		$815.4814	$815.48	$815.45	$815.60