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	$144.60	4.309%	$150.8308	$150.83	$150.85	$150.80
Purchase #2	$49.49	13.321%	$56.0826	$56.08	$56.10	$56.10
Purchase #3	$19.25	6.806%	$20.5602	$20.56	$20.55	$20.60
Purchase #4	$148.42	3.851%	$154.1357	$154.14	$154.15	$154.10
Purchase #5	$218.94	7.132%	$234.5548	$234.55	$234.55	$234.60
Purchase #6	$48.57	10.426%	$53.6339	$53.63	$53.65	$53.60
Purchase #7	$18.62	8.446%	$20.1926	$20.19	$20.20	$20.20
7 purchase totals =	$647.89		$689.9906	$689.98	$690.05	$690.00