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	$20.40	5.211%	$21.463	$21.46	$21.45	$21.50
Purchase #2	$72.44	10.519%	$80.06	$80.06	$80.05	$80.10
Purchase #3	$136.79	13.443%	$155.1787	$155.18	$155.20	$155.20
Purchase #4	$42.96	6.326%	$45.6776	$45.68	$45.70	$45.70
Purchase #5	$140.30	10.855%	$155.5296	$155.53	$155.55	$155.50
Purchase #6	$15.61	13.863%	$17.774	$17.77	$17.75	$17.80
Purchase #7	$105.75	5.611%	$111.6836	$111.68	$111.70	$111.70
7 purchase totals =	$534.25		$587.3665	$587.36	$587.40	$587.50