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	$97.90	8.136%	$105.8651	$105.87	$105.85	$105.90
Purchase #2	$109.45	7.254%	$117.3895	$117.39	$117.40	$117.40
Purchase #3	$167.72	10.757%	$185.7616	$185.76	$185.75	$185.80
Purchase #4	$161.49	4.298%	$168.4308	$168.43	$168.45	$168.40
Purchase #5	$49.55	5.861%	$52.4541	$52.45	$52.45	$52.50
Purchase #6	$34.99	6.121%	$37.1317	$37.13	$37.15	$37.10
Purchase #7	$17.34	4.238%	$18.0749	$18.07	$18.05	$18.10
7 purchase totals =	$638.44		$685.1077	$685.10	$685.10	$685.20