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	$78.73	6.388%	$83.7593	$83.76	$83.75	$83.80
Purchase #2	$46.48	13.139%	$52.587	$52.59	$52.60	$52.60
Purchase #3	$18.66	3.753%	$19.3603	$19.36	$19.35	$19.40
Purchase #4	$250.45	11.793%	$279.9856	$279.99	$280.00	$280.00
Purchase #5	$46.70	5.474%	$49.2564	$49.26	$49.25	$49.30
Purchase #6	$28.90	7.804%	$31.1554	$31.16	$31.15	$31.20
Purchase #7	$61.35	7.824%	$66.15	$66.15	$66.15	$66.20
7 purchase totals =	$531.27		$582.2540	$582.27	$582.25	$582.50