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	$70.56	9.602%	$77.3352	$77.34	$77.35	$77.30
Purchase #2	$45.31	9.422%	$49.5791	$49.58	$49.60	$49.60
Purchase #3	$118.76	8.299%	$128.6159	$128.62	$128.60	$128.60
Purchase #4	$64.72	10.596%	$71.5777	$71.58	$71.60	$71.60
Purchase #5	$238.52	4.820%	$250.0167	$250.02	$250.00	$250.00
Purchase #6	$153.74	9.493%	$168.3345	$168.33	$168.35	$168.30
Purchase #7	$83.95	12.127%	$94.1306	$94.13	$94.15	$94.10
7 purchase totals =	$775.56		$839.5897	$839.60	$839.65	$839.50