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	$69.97	11.852%	$78.2628	$78.26	$78.25	$78.30
Purchase #2	$123.70	12.276%	$138.8854	$138.89	$138.90	$138.90
Purchase #3	$116.69	5.410%	$123.0029	$123.00	$123.00	$123.00
Purchase #4	$6.50	13.636%	$7.3863	$7.39	$7.40	$7.40
Purchase #5	$143.92	8.357%	$155.9474	$155.95	$155.95	$155.90
Purchase #6	$64.62	6.147%	$68.5922	$68.59	$68.60	$68.60
Purchase #7	$83.55	7.335%	$89.6784	$89.68	$89.70	$89.70
7 purchase totals =	$608.95		$661.7554	$661.76	$661.80	$661.80