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	$179.79	6.442%	$191.3721	$191.37	$191.35	$191.40
Purchase #2	$47.63	10.533%	$52.6469	$52.65	$52.65	$52.60
Purchase #3	$155.37	7.139%	$166.4619	$166.46	$166.45	$166.50
Purchase #4	$206.28	10.141%	$227.1989	$227.20	$227.20	$227.20
Purchase #5	$164.67	3.106%	$169.7847	$169.78	$169.80	$169.80
Purchase #6	$53.49	11.411%	$59.5937	$59.59	$59.60	$59.60
Purchase #7	$112.99	13.617%	$128.3758	$128.38	$128.40	$128.40
7 purchase totals =	$920.22		$995.4340	$995.43	$995.45	$995.50