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	$153.35	8.797%	$166.8402	$166.84	$166.85	$166.80
Purchase #2	$161.55	9.422%	$176.7712	$176.77	$176.75	$176.80
Purchase #3	$39.72	6.590%	$42.3375	$42.34	$42.35	$42.30
Purchase #4	$104.69	7.610%	$112.6569	$112.66	$112.65	$112.70
Purchase #5	$160.64	3.637%	$166.4825	$166.48	$166.50	$166.50
Purchase #6	$132.76	10.353%	$146.5046	$146.50	$146.50	$146.50
Purchase #7	$233.58	10.125%	$257.23	$257.23	$257.25	$257.20
7 purchase totals =	$986.29		$1,068.8229	$1,068.82	$1,068.85	$1,068.80