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	$95.39	11.629%	$106.4829	$106.48	$106.50	$106.50
Purchase #2	$138.91	5.465%	$146.5014	$146.50	$146.50	$146.50
Purchase #3	$29.38	9.168%	$32.0736	$32.07	$32.05	$32.10
Purchase #4	$99.60	6.481%	$106.0551	$106.06	$106.05	$106.10
Purchase #5	$91.85	10.201%	$101.2196	$101.22	$101.20	$101.20
Purchase #6	$34.61	11.653%	$38.6431	$38.64	$38.65	$38.60
Purchase #7	$46.85	7.578%	$50.4003	$50.40	$50.40	$50.40
7 purchase totals =	$536.59		$581.3760	$581.37	$581.35	$581.40