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	$74.32	5.249%	$78.2211	$78.22	$78.20	$78.20
Purchase #2	$40.61	3.745%	$42.1308	$42.13	$42.15	$42.10
Purchase #3	$42.94	4.571%	$44.9028	$44.90	$44.90	$44.90
Purchase #4	$224.83	3.637%	$233.0071	$233.01	$233.00	$233.00
Purchase #5	$132.78	8.628%	$144.2363	$144.24	$144.25	$144.20
Purchase #6	$163.91	13.102%	$185.3855	$185.39	$185.40	$185.40
Purchase #7	$108.40	4.419%	$113.1902	$113.19	$113.20	$113.20
7 purchase totals =	$787.79		$841.0738	$841.08	$841.10	$841.00