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	$243.38	9.663%	$266.8978	$266.90	$266.90	$266.90
Purchase #2	$143.43	4.623%	$150.0608	$150.06	$150.05	$150.10
Purchase #3	$204.85	12.507%	$230.4706	$230.47	$230.45	$230.50
Purchase #4	$211.69	12.563%	$238.2846	$238.28	$238.30	$238.30
Purchase #5	$215.28	8.297%	$233.1418	$233.14	$233.15	$233.10
Purchase #6	$121.83	6.325%	$129.5357	$129.54	$129.55	$129.50
Purchase #7	$84.42	7.123%	$90.4332	$90.43	$90.45	$90.40
7 purchase totals =	$1,224.88		$1,338.8245	$1,338.82	$1,338.85	$1,338.80