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	$80.99	11.467%	$90.2771	$90.28	$90.30	$90.30
Purchase #2	$68.30	6.770%	$72.9239	$72.92	$72.90	$72.90
Purchase #3	$221.82	3.160%	$228.8295	$228.83	$228.85	$228.80
Purchase #4	$48.94	9.736%	$53.7048	$53.70	$53.70	$53.70
Purchase #5	$15.89	4.579%	$16.6176	$16.62	$16.60	$16.60
Purchase #6	$138.58	10.803%	$153.5508	$153.55	$153.55	$153.60
Purchase #7	$206.78	12.721%	$233.0845	$233.08	$233.10	$233.10
7 purchase totals =	$781.30		$848.9882	$848.98	$849.00	$849.00