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	$123.47	11.624%	$137.8222	$137.82	$137.80	$137.80
Purchase #2	$14.41	6.698%	$15.3752	$15.38	$15.40	$15.40
Purchase #3	$146.43	10.179%	$161.3351	$161.34	$161.35	$161.30
Purchase #4	$13.39	13.830%	$15.2418	$15.24	$15.25	$15.20
Purchase #5	$147.67	9.432%	$161.5982	$161.60	$161.60	$161.60
Purchase #6	$46.88	13.790%	$53.3448	$53.34	$53.35	$53.30
Purchase #7	$101.75	9.786%	$111.7073	$111.71	$111.70	$111.70
7 purchase totals =	$594.00		$656.4246	$656.43	$656.45	$656.30