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	$21.74	12.593%	$24.4777	$24.48	$24.50	$24.50
Purchase #2	$62.98	3.442%	$65.1478	$65.15	$65.15	$65.10
Purchase #3	$57.93	5.751%	$61.2616	$61.26	$61.25	$61.30
Purchase #4	$173.88	11.127%	$193.2276	$193.23	$193.25	$193.20
Purchase #5	$88.31	11.707%	$98.6485	$98.65	$98.65	$98.60
Purchase #6	$105.69	12.504%	$118.9055	$118.91	$118.90	$118.90
Purchase #7	$68.36	13.854%	$77.8306	$77.83	$77.85	$77.80
7 purchase totals =	$578.89		$639.4993	$639.51	$639.55	$639.40