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	$230.80	5.136%	$242.6539	$242.65	$242.65	$242.70
Purchase #2	$211.82	13.580%	$240.5852	$240.59	$240.60	$240.60
Purchase #3	$81.25	6.123%	$86.2249	$86.22	$86.20	$86.20
Purchase #4	$38.42	7.195%	$41.1843	$41.18	$41.20	$41.20
Purchase #5	$227.37	4.681%	$238.0132	$238.01	$238.00	$238.00
Purchase #6	$114.85	11.161%	$127.6684	$127.67	$127.65	$127.70
Purchase #7	$60.47	8.280%	$65.4769	$65.48	$65.50	$65.50
7 purchase totals =	$964.98		$1,041.8068	$1,041.80	$1,041.80	$1,041.90