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	$111.57	8.301%	$120.8314	$120.83	$120.85	$120.80
Purchase #2	$72.47	7.624%	$77.9951	$78.00	$78.00	$78.00
Purchase #3	$128.52	9.733%	$141.0289	$141.03	$141.05	$141.00
Purchase #4	$18.85	13.510%	$21.3966	$21.40	$21.40	$21.40
Purchase #5	$55.86	7.310%	$59.9434	$59.94	$59.95	$59.90
Purchase #6	$241.34	11.295%	$268.5994	$268.60	$268.60	$268.60
Purchase #7	$43.25	3.133%	$44.605	$44.61	$44.60	$44.60
7 purchase totals =	$671.86		$734.3998	$734.41	$734.45	$734.30