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	$111.93	4.661%	$117.1471	$117.15	$117.15	$117.10
Purchase #2	$164.98	7.195%	$176.8503	$176.85	$176.85	$176.90
Purchase #3	$113.72	11.749%	$127.081	$127.08	$127.10	$127.10
Purchase #4	$207.33	12.621%	$233.4971	$233.50	$233.50	$233.50
Purchase #5	$131.39	6.236%	$139.5835	$139.58	$139.60	$139.60
Purchase #6	$15.34	9.576%	$16.809	$16.81	$16.80	$16.80
Purchase #7	$170.47	6.130%	$180.9198	$180.92	$180.90	$180.90
7 purchase totals =	$915.16		$991.8878	$991.89	$991.90	$991.90