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	$77.42	10.119%	$85.2541	$85.25	$85.25	$85.30
Purchase #2	$111.69	11.795%	$124.8638	$124.86	$124.85	$124.90
Purchase #3	$249.32	12.250%	$279.8617	$279.86	$279.85	$279.90
Purchase #4	$146.34	3.758%	$151.8395	$151.84	$151.85	$151.80
Purchase #5	$39.96	6.471%	$42.5458	$42.55	$42.55	$42.50
Purchase #6	$32.38	12.763%	$36.5127	$36.51	$36.50	$36.50
Purchase #7	$68.52	11.543%	$76.4293	$76.43	$76.45	$76.40
7 purchase totals =	$725.63		$797.3069	$797.30	$797.30	$797.30