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	$239.48	6.812%	$255.7934	$255.79	$255.80	$255.80
Purchase #2	$168.38	13.781%	$191.5844	$191.58	$191.60	$191.60
Purchase #3	$214.97	13.381%	$243.7351	$243.74	$243.75	$243.70
Purchase #4	$34.65	10.698%	$38.3569	$38.36	$38.35	$38.40
Purchase #5	$156.28	11.786%	$174.6992	$174.70	$174.70	$174.70
Purchase #6	$66.83	5.514%	$70.515	$70.52	$70.50	$70.50
Purchase #7	$126.31	8.132%	$136.5815	$136.58	$136.60	$136.60
7 purchase totals =	$1,006.90		$1,111.2655	$1,111.27	$1,111.30	$1,111.30