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	$187.29	12.856%	$211.368	$211.37	$211.35	$211.40
Purchase #2	$100.50	5.327%	$105.8536	$105.85	$105.85	$105.90
Purchase #3	$48.91	7.223%	$52.4428	$52.44	$52.45	$52.40
Purchase #4	$134.80	12.823%	$152.0854	$152.09	$152.10	$152.10
Purchase #5	$87.43	3.556%	$90.539	$90.54	$90.55	$90.50
Purchase #6	$246.97	8.636%	$268.2983	$268.30	$268.30	$268.30
Purchase #7	$103.57	7.531%	$111.3699	$111.37	$111.35	$111.40
7 purchase totals =	$909.47		$991.9570	$991.96	$991.95	$992.00