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	$54.39	12.733%	$61.3155	$61.32	$61.30	$61.30
Purchase #2	$70.80	10.802%	$78.4478	$78.45	$78.45	$78.40
Purchase #3	$170.94	5.540%	$180.4101	$180.41	$180.40	$180.40
Purchase #4	$93.64	10.671%	$103.6323	$103.63	$103.65	$103.60
Purchase #5	$200.69	3.303%	$207.3188	$207.32	$207.30	$207.30
Purchase #6	$82.57	6.251%	$87.7315	$87.73	$87.75	$87.70
Purchase #7	$128.89	10.170%	$141.9981	$142.00	$142.00	$142.00
7 purchase totals =	$801.92		$860.8541	$860.86	$860.85	$860.70