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	$34.72	12.466%	$39.0482	$39.05	$39.05	$39.00
Purchase #2	$10.64	7.733%	$11.4628	$11.46	$11.45	$11.50
Purchase #3	$22.73	10.208%	$25.0503	$25.05	$25.05	$25.10
Purchase #4	$216.56	4.113%	$225.4671	$225.47	$225.45	$225.50
Purchase #5	$186.61	5.285%	$196.4723	$196.47	$196.45	$196.50
Purchase #6	$205.80	6.426%	$219.0247	$219.02	$219.00	$219.00
Purchase #7	$64.54	13.326%	$73.1406	$73.14	$73.15	$73.10
7 purchase totals =	$741.60		$789.6660	$789.66	$789.60	$789.70