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	$166.45	9.433%	$182.1512	$182.15	$182.15	$182.20
Purchase #2	$141.79	8.470%	$153.7996	$153.80	$153.80	$153.80
Purchase #3	$177.39	6.139%	$188.28	$188.28	$188.30	$188.30
Purchase #4	$247.61	9.402%	$270.8903	$270.89	$270.90	$270.90
Purchase #5	$50.56	6.418%	$53.8049	$53.80	$53.80	$53.80
Purchase #6	$221.62	6.256%	$235.4845	$235.48	$235.50	$235.50
Purchase #7	$14.85	3.116%	$15.3127	$15.31	$15.30	$15.30
7 purchase totals =	$1,020.27		$1,099.7232	$1,099.71	$1,099.75	$1,099.80