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	$145.37	6.747%	$155.1781	$155.18	$155.20	$155.20
Purchase #2	$208.47	7.649%	$224.4159	$224.42	$224.40	$224.40
Purchase #3	$111.70	10.343%	$123.2531	$123.25	$123.25	$123.30
Purchase #4	$230.95	4.427%	$241.1742	$241.17	$241.15	$241.20
Purchase #5	$128.42	12.732%	$144.7704	$144.77	$144.75	$144.80
Purchase #6	$62.78	7.600%	$67.5513	$67.55	$67.55	$67.60
Purchase #7	$59.94	11.505%	$66.8361	$66.84	$66.85	$66.80
7 purchase totals =	$947.63		$1,023.1791	$1,023.18	$1,023.15	$1,023.30