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	$95.54	7.801%	$102.9931	$102.99	$103.00	$103.00
Purchase #2	$19.60	4.237%	$20.4305	$20.43	$20.45	$20.40
Purchase #3	$23.37	10.131%	$25.7376	$25.74	$25.75	$25.70
Purchase #4	$45.65	9.748%	$50.1	$50.10	$50.10	$50.10
Purchase #5	$140.77	6.865%	$150.4339	$150.43	$150.45	$150.40
Purchase #6	$113.59	12.513%	$127.8035	$127.80	$127.80	$127.80
Purchase #7	$144.29	8.692%	$156.8317	$156.83	$156.85	$156.80
7 purchase totals =	$582.81		$634.3303	$634.32	$634.40	$634.20