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	$123.52	6.602%	$131.6748	$131.67	$131.65	$131.70
Purchase #2	$64.73	11.464%	$72.1506	$72.15	$72.15	$72.20
Purchase #3	$228.60	11.650%	$255.2319	$255.23	$255.25	$255.20
Purchase #4	$111.31	10.854%	$123.3916	$123.39	$123.40	$123.40
Purchase #5	$52.50	8.196%	$56.8029	$56.80	$56.80	$56.80
Purchase #6	$247.83	12.349%	$278.4345	$278.43	$278.45	$278.40
Purchase #7	$102.61	8.773%	$111.612	$111.61	$111.60	$111.60
7 purchase totals =	$931.10		$1,029.2983	$1,029.28	$1,029.30	$1,029.30