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	$20.55	8.720%	$22.342	$22.34	$22.35	$22.30
Purchase #2	$165.80	6.420%	$176.4444	$176.44	$176.45	$176.40
Purchase #3	$180.80	8.625%	$196.394	$196.39	$196.40	$196.40
Purchase #4	$48.74	3.446%	$50.4196	$50.42	$50.40	$50.40
Purchase #5	$118.40	7.538%	$127.325	$127.33	$127.35	$127.30
Purchase #6	$42.38	10.574%	$46.8613	$46.86	$46.85	$46.90
Purchase #7	$159.67	8.397%	$173.0775	$173.08	$173.10	$173.10
7 purchase totals =	$736.34		$792.8638	$792.86	$792.90	$792.80