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	$38.34	12.739%	$43.2241	$43.22	$43.20	$43.20
Purchase #2	$118.77	5.693%	$125.5316	$125.53	$125.55	$125.50
Purchase #3	$54.76	13.753%	$62.2911	$62.29	$62.30	$62.30
Purchase #4	$88.33	13.494%	$100.2493	$100.25	$100.25	$100.20
Purchase #5	$9.52	6.410%	$10.1302	$10.13	$10.15	$10.10
Purchase #6	$124.37	3.350%	$128.5364	$128.54	$128.55	$128.50
Purchase #7	$194.81	5.714%	$205.9414	$205.94	$205.95	$205.90
7 purchase totals =	$628.90		$675.9041	$675.90	$675.95	$675.70