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	$85.32	4.321%	$89.0067	$89.01	$89.00	$89.00
Purchase #2	$142.43	10.526%	$157.4222	$157.42	$157.40	$157.40
Purchase #3	$75.64	7.532%	$81.3372	$81.34	$81.35	$81.30
Purchase #4	$166.93	11.355%	$185.8849	$185.88	$185.90	$185.90
Purchase #5	$25.71	13.267%	$29.1209	$29.12	$29.10	$29.10
Purchase #6	$96.29	9.853%	$105.7775	$105.78	$105.80	$105.80
Purchase #7	$204.97	11.757%	$229.0683	$229.07	$229.05	$229.10
7 purchase totals =	$797.29		$877.6177	$877.62	$877.60	$877.60