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	$5.84	9.104%	$6.3717	$6.37	$6.35	$6.40
Purchase #2	$53.44	7.122%	$57.246	$57.25	$57.25	$57.20
Purchase #3	$151.54	11.560%	$169.058	$169.06	$169.05	$169.10
Purchase #4	$236.38	8.688%	$256.9167	$256.92	$256.90	$256.90
Purchase #5	$97.99	11.768%	$109.5215	$109.52	$109.50	$109.50
Purchase #6	$28.38	12.117%	$31.8188	$31.82	$31.80	$31.80
Purchase #7	$106.78	4.511%	$111.5968	$111.60	$111.60	$111.60
7 purchase totals =	$680.35		$742.5295	$742.54	$742.45	$742.50