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	$18.61	9.616%	$20.3995	$20.40	$20.40	$20.40
Purchase #2	$175.29	13.153%	$198.3459	$198.35	$198.35	$198.30
Purchase #3	$72.74	10.598%	$80.449	$80.45	$80.45	$80.40
Purchase #4	$11.61	11.217%	$12.9123	$12.91	$12.90	$12.90
Purchase #5	$72.83	5.452%	$76.8007	$76.80	$76.80	$76.80
Purchase #6	$215.43	12.192%	$241.6952	$241.70	$241.70	$241.70
Purchase #7	$139.81	3.620%	$144.8711	$144.87	$144.85	$144.90
7 purchase totals =	$706.32		$775.4737	$775.48	$775.45	$775.40