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	$9.76	5.632%	$10.3097	$10.31	$10.30	$10.30
Purchase #2	$94.48	3.578%	$97.8605	$97.86	$97.85	$97.90
Purchase #3	$68.88	8.479%	$74.7203	$74.72	$74.70	$74.70
Purchase #4	$51.77	5.593%	$54.6655	$54.67	$54.65	$54.70
Purchase #5	$82.72	10.468%	$91.3791	$91.38	$91.40	$91.40
Purchase #6	$48.98	10.592%	$54.168	$54.17	$54.15	$54.20
Purchase #7	$37.55	10.163%	$41.3662	$41.37	$41.35	$41.40
7 purchase totals =	$394.14		$424.4693	$424.48	$424.40	$424.60