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	$248.92	13.611%	$282.8005	$282.80	$282.80	$282.80
Purchase #2	$20.82	11.361%	$23.1854	$23.19	$23.20	$23.20
Purchase #3	$224.45	7.735%	$241.8112	$241.81	$241.80	$241.80
Purchase #4	$81.76	9.262%	$89.3326	$89.33	$89.35	$89.30
Purchase #5	$46.74	9.871%	$51.3537	$51.35	$51.35	$51.40
Purchase #6	$179.97	7.138%	$192.8163	$192.82	$192.80	$192.80
Purchase #7	$121.93	4.298%	$127.1706	$127.17	$127.15	$127.20
7 purchase totals =	$924.59		$1,008.4703	$1,008.47	$1,008.45	$1,008.50