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	$79.33	13.379%	$89.9436	$89.94	$89.95	$89.90
Purchase #2	$238.88	5.580%	$252.2095	$252.21	$252.20	$252.20
Purchase #3	$235.55	7.640%	$253.546	$253.55	$253.55	$253.50
Purchase #4	$225.92	12.153%	$253.3761	$253.38	$253.40	$253.40
Purchase #5	$141.83	12.734%	$159.8906	$159.89	$159.90	$159.90
Purchase #6	$172.47	9.476%	$188.8133	$188.81	$188.80	$188.80
Purchase #7	$172.31	4.178%	$179.5091	$179.51	$179.50	$179.50
7 purchase totals =	$1,266.29		$1,377.2882	$1,377.29	$1,377.30	$1,377.20