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	$104.28	9.141%	$113.8122	$113.81	$113.80	$113.80
Purchase #2	$43.89	4.337%	$45.7935	$45.79	$45.80	$45.80
Purchase #3	$127.57	9.160%	$139.2554	$139.26	$139.25	$139.30
Purchase #4	$40.46	7.366%	$43.4403	$43.44	$43.45	$43.40
Purchase #5	$172.49	13.777%	$196.2539	$196.25	$196.25	$196.30
Purchase #6	$78.77	3.608%	$81.612	$81.61	$81.60	$81.60
Purchase #7	$11.84	12.646%	$13.3373	$13.34	$13.35	$13.30
7 purchase totals =	$579.30		$633.5046	$633.50	$633.50	$633.50