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	$54.78	3.793%	$56.8578	$56.86	$56.85	$56.90
Purchase #2	$45.97	5.415%	$48.4593	$48.46	$48.45	$48.50
Purchase #3	$56.47	8.351%	$61.1858	$61.19	$61.20	$61.20
Purchase #4	$32.80	11.128%	$36.45	$36.45	$36.45	$36.50
Purchase #5	$229.85	12.506%	$258.595	$258.60	$258.60	$258.60
Purchase #6	$47.82	11.670%	$53.4006	$53.40	$53.40	$53.40
Purchase #7	$94.91	3.577%	$98.3049	$98.30	$98.30	$98.30
7 purchase totals =	$562.60		$613.2534	$613.26	$613.25	$613.40