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	$228.59	11.849%	$255.6756	$255.68	$255.70	$255.70
Purchase #2	$189.72	11.377%	$211.3044	$211.30	$211.30	$211.30
Purchase #3	$30.79	10.368%	$33.9823	$33.98	$34.00	$34.00
Purchase #4	$115.34	7.102%	$123.5314	$123.53	$123.55	$123.50
Purchase #5	$12.97	3.594%	$13.4361	$13.44	$13.45	$13.40
Purchase #6	$40.90	5.286%	$43.062	$43.06	$43.05	$43.10
Purchase #7	$157.86	9.211%	$172.4005	$172.40	$172.40	$172.40
7 purchase totals =	$776.17		$853.3923	$853.39	$853.45	$853.40