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	$40.89	3.723%	$42.4123	$42.41	$42.40	$42.40
Purchase #2	$83.60	7.157%	$89.5833	$89.58	$89.60	$89.60
Purchase #3	$41.80	10.659%	$46.2555	$46.26	$46.25	$46.30
Purchase #4	$29.28	3.627%	$30.342	$30.34	$30.35	$30.30
Purchase #5	$174.95	5.746%	$185.0026	$185.00	$185.00	$185.00
Purchase #6	$122.88	9.283%	$134.287	$134.29	$134.30	$134.30
Purchase #7	$224.95	11.153%	$250.0387	$250.04	$250.05	$250.00
7 purchase totals =	$718.35		$777.9214	$777.92	$777.95	$777.90