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	$38.67	8.570%	$41.984	$41.98	$42.00	$42.00
Purchase #2	$45.50	6.820%	$48.6031	$48.60	$48.60	$48.60
Purchase #3	$125.92	9.808%	$138.2702	$138.27	$138.25	$138.30
Purchase #4	$80.49	11.301%	$89.5862	$89.59	$89.60	$89.60
Purchase #5	$92.46	9.747%	$101.4721	$101.47	$101.45	$101.50
Purchase #6	$15.76	11.581%	$17.5852	$17.59	$17.60	$17.60
Purchase #7	$118.64	12.494%	$133.4629	$133.46	$133.45	$133.50
7 purchase totals =	$517.44		$570.9637	$570.96	$570.95	$571.10