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	$98.55	5.597%	$104.0658	$104.07	$104.05	$104.10
Purchase #2	$242.27	5.823%	$256.3774	$256.38	$256.40	$256.40
Purchase #3	$158.77	4.469%	$165.8654	$165.87	$165.85	$165.90
Purchase #4	$65.42	13.632%	$74.3381	$74.34	$74.35	$74.30
Purchase #5	$18.88	6.345%	$20.0779	$20.08	$20.10	$20.10
Purchase #6	$38.76	3.391%	$40.0744	$40.07	$40.05	$40.10
Purchase #7	$47.37	7.533%	$50.9384	$50.94	$50.95	$50.90
7 purchase totals =	$670.02		$711.7374	$711.75	$711.75	$711.80