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	$112.69	6.745%	$120.2909	$120.29	$120.30	$120.30
Purchase #2	$41.75	11.127%	$46.3955	$46.40	$46.40	$46.40
Purchase #3	$81.42	11.320%	$90.6367	$90.64	$90.65	$90.60
Purchase #4	$158.63	4.451%	$165.6906	$165.69	$165.70	$165.70
Purchase #5	$52.85	4.566%	$55.2631	$55.26	$55.25	$55.30
Purchase #6	$174.78	4.448%	$182.5542	$182.55	$182.55	$182.60
Purchase #7	$230.49	11.636%	$257.3098	$257.31	$257.30	$257.30
7 purchase totals =	$852.61		$918.1408	$918.14	$918.15	$918.20