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	$121.35	4.204%	$126.4516	$126.45	$126.45	$126.50
Purchase #2	$136.77	3.474%	$141.5214	$141.52	$141.50	$141.50
Purchase #3	$101.69	4.510%	$106.2762	$106.28	$106.30	$106.30
Purchase #4	$18.76	12.836%	$21.168	$21.17	$21.15	$21.20
Purchase #5	$159.26	4.236%	$166.0063	$166.01	$166.00	$166.00
Purchase #6	$16.39	12.523%	$18.4425	$18.44	$18.45	$18.40
Purchase #7	$52.71	12.703%	$59.4058	$59.41	$59.40	$59.40
7 purchase totals =	$606.93		$639.2718	$639.28	$639.25	$639.30