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	$133.66	13.381%	$151.545	$151.55	$151.55	$151.50
Purchase #2	$207.42	9.784%	$227.714	$227.71	$227.70	$227.70
Purchase #3	$86.56	5.446%	$91.2741	$91.27	$91.25	$91.30
Purchase #4	$17.73	3.562%	$18.3615	$18.36	$18.35	$18.40
Purchase #5	$243.80	11.627%	$272.1466	$272.15	$272.15	$272.10
Purchase #6	$78.68	12.660%	$88.6409	$88.64	$88.65	$88.60
Purchase #7	$111.81	10.550%	$123.606	$123.61	$123.60	$123.60
7 purchase totals =	$879.66		$973.2881	$973.29	$973.25	$973.20