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	$42.60	7.593%	$45.8346	$45.83	$45.85	$45.80
Purchase #2	$91.98	8.771%	$100.0476	$100.05	$100.05	$100.00
Purchase #3	$151.72	3.628%	$157.2244	$157.22	$157.20	$157.20
Purchase #4	$15.76	10.419%	$17.402	$17.40	$17.40	$17.40
Purchase #5	$94.96	5.756%	$100.4259	$100.43	$100.45	$100.40
Purchase #6	$205.82	12.412%	$231.3664	$231.37	$231.35	$231.40
Purchase #7	$233.29	13.637%	$265.1038	$265.10	$265.10	$265.10
7 purchase totals =	$836.13		$917.4047	$917.40	$917.40	$917.30