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	$71.95	10.422%	$79.4486	$79.45	$79.45	$79.40
Purchase #2	$151.93	6.306%	$161.5107	$161.51	$161.50	$161.50
Purchase #3	$80.54	11.740%	$89.9954	$90.00	$90.00	$90.00
Purchase #4	$27.47	3.693%	$28.4845	$28.48	$28.50	$28.50
Purchase #5	$235.47	8.345%	$255.12	$255.12	$255.10	$255.10
Purchase #6	$149.82	8.215%	$162.1277	$162.13	$162.15	$162.10
Purchase #7	$240.49	9.267%	$262.7762	$262.78	$262.80	$262.80
7 purchase totals =	$957.67		$1,039.4631	$1,039.47	$1,039.50	$1,039.40