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	$234.58	10.363%	$258.8895	$258.89	$258.90	$258.90
Purchase #2	$63.80	10.425%	$70.4512	$70.45	$70.45	$70.50
Purchase #3	$53.33	8.427%	$57.8241	$57.82	$57.80	$57.80
Purchase #4	$47.36	3.226%	$48.8878	$48.89	$48.90	$48.90
Purchase #5	$208.66	11.692%	$233.0565	$233.06	$233.05	$233.10
Purchase #6	$35.53	11.613%	$39.6561	$39.66	$39.65	$39.70
Purchase #7	$118.42	4.199%	$123.3925	$123.39	$123.40	$123.40
7 purchase totals =	$761.68		$832.1577	$832.16	$832.15	$832.30