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	$56.56	12.269%	$63.4993	$63.50	$63.50	$63.50
Purchase #2	$169.43	9.499%	$185.5242	$185.52	$185.50	$185.50
Purchase #3	$139.47	5.425%	$147.0362	$147.04	$147.05	$147.00
Purchase #4	$119.77	6.706%	$127.8018	$127.80	$127.80	$127.80
Purchase #5	$20.76	11.326%	$23.1113	$23.11	$23.10	$23.10
Purchase #6	$37.35	11.724%	$41.7289	$41.73	$41.75	$41.70
Purchase #7	$212.82	8.824%	$231.5992	$231.60	$231.60	$231.60
7 purchase totals =	$756.16		$820.3009	$820.30	$820.30	$820.20