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	$36.34	11.165%	$40.3974	$40.40	$40.40	$40.40
Purchase #2	$230.89	13.537%	$262.1456	$262.15	$262.15	$262.10
Purchase #3	$162.59	6.141%	$172.5747	$172.57	$172.55	$172.60
Purchase #4	$110.93	8.524%	$120.3857	$120.39	$120.40	$120.40
Purchase #5	$49.83	12.732%	$56.1744	$56.17	$56.15	$56.20
Purchase #6	$92.68	8.406%	$100.4707	$100.47	$100.45	$100.50
Purchase #7	$133.34	12.556%	$150.0822	$150.08	$150.10	$150.10
7 purchase totals =	$816.60		$902.2307	$902.23	$902.20	$902.30