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	$17.55	10.222%	$19.344	$19.34	$19.35	$19.30
Purchase #2	$237.26	4.749%	$248.5275	$248.53	$248.55	$248.50
Purchase #3	$24.40	11.860%	$27.2938	$27.29	$27.30	$27.30
Purchase #4	$133.45	5.683%	$141.034	$141.03	$141.05	$141.00
Purchase #5	$73.49	13.660%	$83.5287	$83.53	$83.55	$83.50
Purchase #6	$59.59	9.845%	$65.4566	$65.46	$65.45	$65.50
Purchase #7	$27.34	3.346%	$28.2548	$28.25	$28.25	$28.30
7 purchase totals =	$573.08		$613.4394	$613.43	$613.50	$613.40