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	$64.93	12.722%	$73.1904	$73.19	$73.20	$73.20
Purchase #2	$95.39	5.581%	$100.7137	$100.71	$100.70	$100.70
Purchase #3	$153.52	4.659%	$160.6725	$160.67	$160.65	$160.70
Purchase #4	$78.45	13.584%	$89.1066	$89.11	$89.10	$89.10
Purchase #5	$40.29	8.475%	$43.7046	$43.70	$43.70	$43.70
Purchase #6	$98.74	10.292%	$108.9023	$108.90	$108.90	$108.90
Purchase #7	$109.32	7.135%	$117.12	$117.12	$117.10	$117.10
7 purchase totals =	$640.64		$693.4101	$693.40	$693.35	$693.40