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	$34.85	8.363%	$37.7645	$37.76	$37.75	$37.80
Purchase #2	$58.58	13.727%	$66.6213	$66.62	$66.60	$66.60
Purchase #3	$177.69	10.349%	$196.0791	$196.08	$196.10	$196.10
Purchase #4	$120.72	9.172%	$131.7924	$131.79	$131.80	$131.80
Purchase #5	$168.87	13.362%	$191.4344	$191.43	$191.45	$191.40
Purchase #6	$97.37	9.661%	$106.7769	$106.78	$106.80	$106.80
Purchase #7	$237.44	4.292%	$247.6309	$247.63	$247.65	$247.60
7 purchase totals =	$895.52		$978.0995	$978.09	$978.15	$978.10