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	$153.43	12.285%	$172.2789	$172.28	$172.30	$172.30
Purchase #2	$47.82	9.855%	$52.5327	$52.53	$52.55	$52.50
Purchase #3	$79.25	8.676%	$86.1257	$86.13	$86.15	$86.10
Purchase #4	$71.26	9.869%	$78.2926	$78.29	$78.30	$78.30
Purchase #5	$68.97	5.527%	$72.782	$72.78	$72.80	$72.80
Purchase #6	$154.94	3.422%	$160.242	$160.24	$160.25	$160.20
Purchase #7	$240.83	7.720%	$259.4221	$259.42	$259.40	$259.40
7 purchase totals =	$816.50		$881.6760	$881.67	$881.75	$881.60