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	$21.32	13.670%	$24.2344	$24.23	$24.25	$24.20
Purchase #2	$46.78	9.649%	$51.2938	$51.29	$51.30	$51.30
Purchase #3	$16.63	4.243%	$17.3356	$17.34	$17.35	$17.30
Purchase #4	$118.72	10.794%	$131.5346	$131.53	$131.55	$131.50
Purchase #5	$18.95	8.345%	$20.5314	$20.53	$20.55	$20.50
Purchase #6	$150.27	4.834%	$157.5341	$157.53	$157.55	$157.50
Purchase #7	$82.91	6.712%	$88.4749	$88.47	$88.45	$88.50
7 purchase totals =	$455.58		$490.9388	$490.92	$491.00	$490.80