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	$134.54	13.229%	$152.3383	$152.34	$152.35	$152.30
Purchase #2	$122.94	12.323%	$138.0899	$138.09	$138.10	$138.10
Purchase #3	$47.67	8.295%	$51.6242	$51.62	$51.60	$51.60
Purchase #4	$112.65	13.295%	$127.6268	$127.63	$127.65	$127.60
Purchase #5	$162.47	8.592%	$176.4294	$176.43	$176.45	$176.40
Purchase #6	$139.93	5.134%	$147.114	$147.11	$147.10	$147.10
Purchase #7	$79.66	13.750%	$90.6133	$90.61	$90.60	$90.60
7 purchase totals =	$799.86		$883.8359	$883.83	$883.85	$883.70