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	$84.63	6.566%	$90.1868	$90.19	$90.20	$90.20
Purchase #2	$241.65	5.819%	$255.7116	$255.71	$255.70	$255.70
Purchase #3	$78.46	4.638%	$82.099	$82.10	$82.10	$82.10
Purchase #4	$243.67	11.231%	$271.0366	$271.04	$271.05	$271.00
Purchase #5	$50.98	13.370%	$57.796	$57.80	$57.80	$57.80
Purchase #6	$50.35	12.759%	$56.7742	$56.77	$56.75	$56.80
Purchase #7	$64.66	11.622%	$72.1748	$72.17	$72.15	$72.20
7 purchase totals =	$814.40		$885.7790	$885.78	$885.75	$885.80