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	$50.78	12.196%	$56.9731	$56.97	$56.95	$57.00
Purchase #2	$30.33	7.463%	$32.5935	$32.59	$32.60	$32.60
Purchase #3	$50.77	12.166%	$56.9467	$56.95	$56.95	$56.90
Purchase #4	$237.44	8.854%	$258.4629	$258.46	$258.45	$258.50
Purchase #5	$13.36	6.703%	$14.2555	$14.26	$14.25	$14.30
Purchase #6	$212.62	4.326%	$221.8179	$221.82	$221.80	$221.80
Purchase #7	$122.28	4.236%	$127.4598	$127.46	$127.45	$127.50
7 purchase totals =	$717.58		$768.5094	$768.51	$768.45	$768.60