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	$27.90	4.480%	$29.1499	$29.15	$29.15	$29.10
Purchase #2	$102.56	10.255%	$113.0775	$113.08	$113.10	$113.10
Purchase #3	$190.43	13.739%	$216.5932	$216.59	$216.60	$216.60
Purchase #4	$124.40	10.601%	$137.5876	$137.59	$137.60	$137.60
Purchase #5	$138.28	4.122%	$143.9799	$143.98	$144.00	$144.00
Purchase #6	$67.95	5.630%	$71.7756	$71.78	$71.80	$71.80
Purchase #7	$36.66	10.545%	$40.5258	$40.53	$40.55	$40.50
7 purchase totals =	$688.18		$752.6895	$752.70	$752.80	$752.70