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	$82.26	9.630%	$90.1816	$90.18	$90.20	$90.20
Purchase #2	$228.92	13.479%	$259.7761	$259.78	$259.80	$259.80
Purchase #3	$37.25	13.229%	$42.1778	$42.18	$42.20	$42.20
Purchase #4	$104.95	12.468%	$118.0352	$118.04	$118.05	$118.00
Purchase #5	$72.75	4.669%	$76.1467	$76.15	$76.15	$76.10
Purchase #6	$76.37	11.662%	$85.2763	$85.28	$85.30	$85.30
Purchase #7	$115.59	7.805%	$124.6118	$124.61	$124.60	$124.60
7 purchase totals =	$718.09		$796.2055	$796.22	$796.30	$796.20