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	$44.52	6.664%	$47.4868	$47.49	$47.50	$47.50
Purchase #2	$143.29	13.171%	$162.1627	$162.16	$162.15	$162.20
Purchase #3	$116.28	6.573%	$123.9231	$123.92	$123.90	$123.90
Purchase #4	$248.28	10.637%	$274.6895	$274.69	$274.70	$274.70
Purchase #5	$106.53	4.496%	$111.3196	$111.32	$111.30	$111.30
Purchase #6	$84.68	12.653%	$95.3946	$95.39	$95.40	$95.40
Purchase #7	$121.52	10.775%	$134.6138	$134.61	$134.60	$134.60
7 purchase totals =	$865.10		$949.5901	$949.58	$949.55	$949.60