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	$87.72	13.303%	$99.3894	$99.39	$99.40	$99.40
Purchase #2	$246.75	11.176%	$274.3268	$274.33	$274.35	$274.30
Purchase #3	$217.64	12.462%	$244.7623	$244.76	$244.75	$244.80
Purchase #4	$27.58	6.596%	$29.3992	$29.40	$29.40	$29.40
Purchase #5	$184.29	4.246%	$192.115	$192.12	$192.10	$192.10
Purchase #6	$18.98	12.712%	$21.3927	$21.39	$21.40	$21.40
Purchase #7	$234.31	6.679%	$249.9596	$249.96	$249.95	$250.00
7 purchase totals =	$1,017.27		$1,111.3450	$1,111.35	$1,111.35	$1,111.40