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	$129.57	6.686%	$138.2331	$138.23	$138.25	$138.20
Purchase #2	$172.46	10.410%	$190.4131	$190.41	$190.40	$190.40
Purchase #3	$100.72	10.756%	$111.5534	$111.55	$111.55	$111.60
Purchase #4	$153.87	4.534%	$160.8465	$160.85	$160.85	$160.80
Purchase #5	$19.99	3.720%	$20.7336	$20.73	$20.75	$20.70
Purchase #6	$117.50	8.635%	$127.6461	$127.65	$127.65	$127.60
Purchase #7	$30.58	8.754%	$33.257	$33.26	$33.25	$33.30
7 purchase totals =	$724.69		$782.6828	$782.68	$782.70	$782.60