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	$122.82	11.733%	$137.2305	$137.23	$137.25	$137.20
Purchase #2	$165.47	3.678%	$171.556	$171.56	$171.55	$171.60
Purchase #3	$71.78	8.156%	$77.6344	$77.63	$77.65	$77.60
Purchase #4	$219.56	8.821%	$238.9274	$238.93	$238.95	$238.90
Purchase #5	$61.48	8.866%	$66.9308	$66.93	$66.95	$66.90
Purchase #6	$142.90	3.823%	$148.3631	$148.36	$148.35	$148.40
Purchase #7	$21.85	12.159%	$24.5067	$24.51	$24.50	$24.50
7 purchase totals =	$805.86		$865.1489	$865.15	$865.20	$865.10