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	$66.30	6.470%	$70.5896	$70.59	$70.60	$70.60
Purchase #2	$9.92	9.222%	$10.8348	$10.83	$10.85	$10.80
Purchase #3	$192.56	8.261%	$208.4674	$208.47	$208.45	$208.50
Purchase #4	$140.61	11.230%	$156.4005	$156.40	$156.40	$156.40
Purchase #5	$218.76	9.370%	$239.2578	$239.26	$239.25	$239.30
Purchase #6	$114.87	3.544%	$118.941	$118.94	$118.95	$118.90
Purchase #7	$80.41	12.119%	$90.1549	$90.15	$90.15	$90.20
7 purchase totals =	$823.43		$894.6460	$894.64	$894.65	$894.70