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	$127.38	5.563%	$134.4661	$134.47	$134.45	$134.50
Purchase #2	$146.41	6.834%	$156.4157	$156.42	$156.40	$156.40
Purchase #3	$241.31	13.150%	$273.0423	$273.04	$273.05	$273.00
Purchase #4	$16.72	5.831%	$17.6949	$17.69	$17.70	$17.70
Purchase #5	$76.62	9.454%	$83.8637	$83.86	$83.85	$83.90
Purchase #6	$37.75	7.584%	$40.613	$40.61	$40.60	$40.60
Purchase #7	$214.89	7.156%	$230.2675	$230.27	$230.25	$230.30
7 purchase totals =	$861.08		$936.3632	$936.36	$936.30	$936.40