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	$29.76	13.137%	$33.6696	$33.67	$33.65	$33.70
Purchase #2	$215.49	13.517%	$244.6178	$244.62	$244.60	$244.60
Purchase #3	$106.57	8.500%	$115.6285	$115.63	$115.65	$115.60
Purchase #4	$49.89	11.643%	$55.6987	$55.70	$55.70	$55.70
Purchase #5	$196.83	9.268%	$215.0722	$215.07	$215.05	$215.10
Purchase #6	$82.71	7.728%	$89.1018	$89.10	$89.10	$89.10
Purchase #7	$44.42	8.290%	$48.1024	$48.10	$48.10	$48.10
7 purchase totals =	$725.67		$801.8910	$801.89	$801.85	$801.90