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	$45.28	13.182%	$51.2488	$51.25	$51.25	$51.20
Purchase #2	$204.37	11.225%	$227.3105	$227.31	$227.30	$227.30
Purchase #3	$101.89	9.758%	$111.8324	$111.83	$111.85	$111.80
Purchase #4	$64.80	11.602%	$72.3181	$72.32	$72.30	$72.30
Purchase #5	$246.91	5.568%	$260.6579	$260.66	$260.65	$260.70
Purchase #6	$201.52	5.201%	$212.0011	$212.00	$212.00	$212.00
Purchase #7	$174.32	12.606%	$196.2948	$196.29	$196.30	$196.30
7 purchase totals =	$1,039.09		$1,131.6636	$1,131.66	$1,131.65	$1,131.60