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	$20.70	3.805%	$21.4876	$21.49	$21.50	$21.50
Purchase #2	$198.69	9.658%	$217.8795	$217.88	$217.90	$217.90
Purchase #3	$11.58	11.579%	$12.9208	$12.92	$12.90	$12.90
Purchase #4	$168.84	6.115%	$179.1646	$179.16	$179.15	$179.20
Purchase #5	$237.72	5.545%	$250.9016	$250.90	$250.90	$250.90
Purchase #6	$235.65	12.240%	$264.4936	$264.49	$264.50	$264.50
Purchase #7	$37.59	13.708%	$42.7428	$42.74	$42.75	$42.70
7 purchase totals =	$910.77		$989.5905	$989.58	$989.60	$989.60