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	$88.25	13.647%	$100.2935	$100.29	$100.30	$100.30
Purchase #2	$46.87	12.105%	$52.5436	$52.54	$52.55	$52.50
Purchase #3	$51.91	9.373%	$56.7755	$56.78	$56.80	$56.80
Purchase #4	$41.64	11.715%	$46.5181	$46.52	$46.50	$46.50
Purchase #5	$15.56	6.558%	$16.5804	$16.58	$16.60	$16.60
Purchase #6	$22.64	9.443%	$24.7779	$24.78	$24.80	$24.80
Purchase #7	$77.68	4.172%	$80.9208	$80.92	$80.90	$80.90
7 purchase totals =	$344.55		$378.4098	$378.41	$378.45	$378.40