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	$100.99	12.622%	$113.737	$113.74	$113.75	$113.70
Purchase #2	$157.78	5.382%	$166.2717	$166.27	$166.25	$166.30
Purchase #3	$44.68	11.683%	$49.9	$49.90	$49.90	$49.90
Purchase #4	$36.86	3.467%	$38.1379	$38.14	$38.15	$38.10
Purchase #5	$89.97	7.204%	$96.4514	$96.45	$96.45	$96.50
Purchase #6	$59.82	3.541%	$61.9382	$61.94	$61.95	$61.90
Purchase #7	$104.83	8.229%	$113.4565	$113.46	$113.45	$113.50
7 purchase totals =	$594.93		$639.8927	$639.90	$639.90	$639.90