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	$11.29	13.509%	$12.8152	$12.82	$12.80	$12.80
Purchase #2	$62.33	13.534%	$70.7657	$70.77	$70.75	$70.80
Purchase #3	$126.35	9.709%	$138.6173	$138.62	$138.60	$138.60
Purchase #4	$159.31	7.813%	$171.7569	$171.76	$171.75	$171.80
Purchase #5	$249.47	11.193%	$277.3932	$277.39	$277.40	$277.40
Purchase #6	$244.55	8.175%	$264.542	$264.54	$264.55	$264.50
Purchase #7	$92.33	9.301%	$100.9176	$100.92	$100.90	$100.90
7 purchase totals =	$945.63		$1,036.8079	$1,036.82	$1,036.75	$1,036.80