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	$116.31	12.133%	$130.4219	$130.42	$130.40	$130.40
Purchase #2	$34.33	10.267%	$37.8547	$37.85	$37.85	$37.90
Purchase #3	$24.59	10.464%	$27.1631	$27.16	$27.15	$27.20
Purchase #4	$18.78	10.860%	$20.8195	$20.82	$20.80	$20.80
Purchase #5	$18.33	7.715%	$19.7442	$19.74	$19.75	$19.70
Purchase #6	$246.80	13.642%	$280.4685	$280.47	$280.45	$280.50
Purchase #7	$62.92	5.440%	$66.3428	$66.34	$66.35	$66.30
7 purchase totals =	$522.06		$582.8147	$582.80	$582.75	$582.80