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	$117.54	5.149%	$123.5921	$123.59	$123.60	$123.60
Purchase #2	$35.97	8.344%	$38.9713	$38.97	$38.95	$39.00
Purchase #3	$103.35	13.606%	$117.4118	$117.41	$117.40	$117.40
Purchase #4	$110.45	6.396%	$117.5144	$117.51	$117.50	$117.50
Purchase #5	$133.91	8.720%	$145.587	$145.59	$145.60	$145.60
Purchase #6	$59.37	10.388%	$65.5374	$65.54	$65.55	$65.50
Purchase #7	$84.93	13.309%	$96.2333	$96.23	$96.25	$96.20
7 purchase totals =	$645.52		$704.8473	$704.84	$704.85	$704.80