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	$233.55	13.687%	$265.516	$265.52	$265.50	$265.50
Purchase #2	$158.64	3.672%	$164.4653	$164.47	$164.45	$164.50
Purchase #3	$123.85	4.408%	$129.3093	$129.31	$129.30	$129.30
Purchase #4	$48.82	13.392%	$55.358	$55.36	$55.35	$55.40
Purchase #5	$39.93	9.779%	$43.8348	$43.83	$43.85	$43.80
Purchase #6	$96.34	7.475%	$103.5414	$103.54	$103.55	$103.50
Purchase #7	$204.50	11.532%	$228.0829	$228.08	$228.10	$228.10
7 purchase totals =	$905.63		$990.1077	$990.11	$990.10	$990.10