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	$126.27	9.275%	$137.9815	$137.98	$138.00	$138.00
Purchase #2	$211.83	12.409%	$238.116	$238.12	$238.10	$238.10
Purchase #3	$111.39	6.206%	$118.3029	$118.30	$118.30	$118.30
Purchase #4	$136.39	12.548%	$153.5042	$153.50	$153.50	$153.50
Purchase #5	$164.66	9.363%	$180.0771	$180.08	$180.10	$180.10
Purchase #6	$208.82	5.139%	$219.5513	$219.55	$219.55	$219.60
Purchase #7	$56.84	9.575%	$62.2824	$62.28	$62.30	$62.30
7 purchase totals =	$1,016.20		$1,109.8154	$1,109.81	$1,109.85	$1,109.90