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	$70.60	10.735%	$78.1789	$78.18	$78.20	$78.20
Purchase #2	$72.92	13.666%	$82.8852	$82.89	$82.90	$82.90
Purchase #3	$185.95	11.730%	$207.7619	$207.76	$207.75	$207.80
Purchase #4	$44.96	6.338%	$47.8096	$47.81	$47.80	$47.80
Purchase #5	$41.46	3.305%	$42.8303	$42.83	$42.85	$42.80
Purchase #6	$127.71	8.521%	$138.5922	$138.59	$138.60	$138.60
Purchase #7	$158.82	10.545%	$175.5676	$175.57	$175.55	$175.60
7 purchase totals =	$702.42		$773.6257	$773.63	$773.65	$773.70