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	$151.38	12.489%	$170.2858	$170.29	$170.30	$170.30
Purchase #2	$225.96	6.661%	$241.0112	$241.01	$241.00	$241.00
Purchase #3	$7.85	4.118%	$8.1733	$8.17	$8.15	$8.20
Purchase #4	$95.72	13.685%	$108.8193	$108.82	$108.80	$108.80
Purchase #5	$165.30	7.123%	$177.0743	$177.07	$177.05	$177.10
Purchase #6	$95.38	8.633%	$103.6142	$103.61	$103.60	$103.60
Purchase #7	$99.58	10.383%	$109.9194	$109.92	$109.90	$109.90
7 purchase totals =	$841.17		$918.8975	$918.89	$918.80	$918.90