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	$7.49	10.455%	$8.2731	$8.27	$8.25	$8.30
Purchase #2	$146.52	3.642%	$151.8563	$151.86	$151.85	$151.90
Purchase #3	$82.81	9.588%	$90.7498	$90.75	$90.75	$90.70
Purchase #4	$82.48	11.289%	$91.7912	$91.79	$91.80	$91.80
Purchase #5	$37.43	7.695%	$40.3102	$40.31	$40.30	$40.30
Purchase #6	$193.79	3.333%	$200.249	$200.25	$200.25	$200.20
Purchase #7	$177.41	12.786%	$200.0936	$200.09	$200.10	$200.10
7 purchase totals =	$727.93		$783.3232	$783.32	$783.30	$783.30