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	$51.64	7.103%	$55.308	$55.31	$55.30	$55.30
Purchase #2	$63.35	10.499%	$70.0011	$70.00	$70.00	$70.00
Purchase #3	$31.61	12.123%	$35.4421	$35.44	$35.45	$35.40
Purchase #4	$74.83	4.319%	$78.0619	$78.06	$78.05	$78.10
Purchase #5	$98.60	5.852%	$104.3701	$104.37	$104.35	$104.40
Purchase #6	$235.94	5.657%	$249.2871	$249.29	$249.30	$249.30
Purchase #7	$195.83	4.297%	$204.2448	$204.24	$204.25	$204.20
7 purchase totals =	$751.80		$796.7151	$796.71	$796.70	$796.70