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	$127.71	8.708%	$138.831	$138.83	$138.85	$138.80
Purchase #2	$238.64	7.587%	$256.7456	$256.75	$256.75	$256.70
Purchase #3	$9.39	12.688%	$10.5814	$10.58	$10.60	$10.60
Purchase #4	$100.36	11.447%	$111.8482	$111.85	$111.85	$111.80
Purchase #5	$161.83	11.156%	$179.8838	$179.88	$179.90	$179.90
Purchase #6	$216.34	5.671%	$228.6086	$228.61	$228.60	$228.60
Purchase #7	$148.58	11.849%	$166.1852	$166.19	$166.20	$166.20
7 purchase totals =	$1,002.85		$1,092.6838	$1,092.69	$1,092.75	$1,092.60