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	$143.93	8.616%	$156.331	$156.33	$156.35	$156.30
Purchase #2	$125.30	4.377%	$130.7844	$130.78	$130.80	$130.80
Purchase #3	$34.54	8.261%	$37.3933	$37.39	$37.40	$37.40
Purchase #4	$120.75	5.542%	$127.442	$127.44	$127.45	$127.40
Purchase #5	$38.64	4.606%	$40.4198	$40.42	$40.40	$40.40
Purchase #6	$178.80	8.587%	$194.1536	$194.15	$194.15	$194.20
Purchase #7	$196.92	11.764%	$220.0857	$220.09	$220.10	$220.10
7 purchase totals =	$838.88		$906.6098	$906.60	$906.65	$906.60