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	$53.79	5.209%	$56.5919	$56.59	$56.60	$56.60
Purchase #2	$84.45	13.488%	$95.8406	$95.84	$95.85	$95.80
Purchase #3	$162.28	3.361%	$167.7342	$167.73	$167.75	$167.70
Purchase #4	$108.93	8.462%	$118.1477	$118.15	$118.15	$118.10
Purchase #5	$19.56	13.655%	$22.2309	$22.23	$22.25	$22.20
Purchase #6	$36.96	12.448%	$41.5608	$41.56	$41.55	$41.60
Purchase #7	$80.70	11.578%	$90.0434	$90.04	$90.05	$90.00
7 purchase totals =	$546.67		$592.1495	$592.14	$592.20	$592.00