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	$114.37	5.705%	$120.8948	$120.89	$120.90	$120.90
Purchase #2	$152.40	9.316%	$166.5976	$166.60	$166.60	$166.60
Purchase #3	$153.48	11.665%	$171.3834	$171.38	$171.40	$171.40
Purchase #4	$95.61	5.170%	$100.553	$100.55	$100.55	$100.60
Purchase #5	$12.71	8.123%	$13.7424	$13.74	$13.75	$13.70
Purchase #6	$228.68	12.856%	$258.0791	$258.08	$258.10	$258.10
Purchase #7	$134.39	13.136%	$152.0435	$152.04	$152.05	$152.00
7 purchase totals =	$891.64		$983.2938	$983.28	$983.35	$983.30