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	$36.75	7.599%	$39.5426	$39.54	$39.55	$39.50
Purchase #2	$45.29	9.364%	$49.531	$49.53	$49.55	$49.50
Purchase #3	$118.55	7.828%	$127.8301	$127.83	$127.85	$127.80
Purchase #4	$188.40	7.446%	$202.4283	$202.43	$202.45	$202.40
Purchase #5	$122.64	7.462%	$131.7914	$131.79	$131.80	$131.80
Purchase #6	$131.94	12.569%	$148.5235	$148.52	$148.50	$148.50
Purchase #7	$111.93	6.547%	$119.2581	$119.26	$119.25	$119.30
7 purchase totals =	$755.50		$818.9050	$818.90	$818.95	$818.80