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	$59.30	12.593%	$66.7676	$66.77	$66.75	$66.80
Purchase #2	$134.71	8.450%	$146.093	$146.09	$146.10	$146.10
Purchase #3	$103.79	11.860%	$116.0995	$116.10	$116.10	$116.10
Purchase #4	$14.26	11.397%	$15.8852	$15.89	$15.90	$15.90
Purchase #5	$40.50	7.440%	$43.5132	$43.51	$43.50	$43.50
Purchase #6	$145.70	3.696%	$151.0851	$151.09	$151.10	$151.10
Purchase #7	$47.99	11.450%	$53.4849	$53.48	$53.50	$53.50
7 purchase totals =	$546.25		$592.9285	$592.93	$592.95	$593.00