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	$123.90	10.417%	$136.8067	$136.81	$136.80	$136.80
Purchase #2	$138.94	8.361%	$150.5568	$150.56	$150.55	$150.60
Purchase #3	$116.77	11.595%	$130.3095	$130.31	$130.30	$130.30
Purchase #4	$35.68	4.708%	$37.3598	$37.36	$37.35	$37.40
Purchase #5	$52.91	3.622%	$54.8264	$54.83	$54.85	$54.80
Purchase #6	$176.91	12.184%	$198.4647	$198.46	$198.45	$198.50
Purchase #7	$163.70	5.177%	$172.1747	$172.17	$172.15	$172.20
7 purchase totals =	$808.81		$880.4986	$880.50	$880.45	$880.60