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	$13.69	11.454%	$15.2581	$15.26	$15.25	$15.30
Purchase #2	$103.76	12.286%	$116.508	$116.51	$116.50	$116.50
Purchase #3	$223.39	10.384%	$246.5868	$246.59	$246.60	$246.60
Purchase #4	$181.41	3.333%	$187.4564	$187.46	$187.45	$187.50
Purchase #5	$16.99	9.306%	$18.5711	$18.57	$18.55	$18.60
Purchase #6	$172.57	3.530%	$178.6617	$178.66	$178.65	$178.70
Purchase #7	$18.34	13.737%	$20.8594	$20.86	$20.85	$20.90
7 purchase totals =	$730.15		$783.9015	$783.91	$783.85	$784.10