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	$67.94	6.566%	$72.4009	$72.40	$72.40	$72.40
Purchase #2	$98.31	4.613%	$102.845	$102.85	$102.85	$102.80
Purchase #3	$222.39	7.693%	$239.4985	$239.50	$239.50	$239.50
Purchase #4	$127.79	9.270%	$139.6361	$139.64	$139.65	$139.60
Purchase #5	$135.81	7.703%	$146.2714	$146.27	$146.25	$146.30
Purchase #6	$184.27	8.558%	$200.0398	$200.04	$200.05	$200.00
Purchase #7	$46.88	7.537%	$50.4133	$50.41	$50.40	$50.40
7 purchase totals =	$883.39		$951.1050	$951.11	$951.10	$951.00