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	$69.49	12.611%	$78.2534	$78.25	$78.25	$78.30
Purchase #2	$23.36	7.873%	$25.1991	$25.20	$25.20	$25.20
Purchase #3	$19.77	12.555%	$22.2521	$22.25	$22.25	$22.30
Purchase #4	$111.73	13.657%	$126.989	$126.99	$127.00	$127.00
Purchase #5	$185.94	5.670%	$196.4828	$196.48	$196.50	$196.50
Purchase #6	$24.31	3.578%	$25.1798	$25.18	$25.20	$25.20
Purchase #7	$112.68	9.561%	$123.4533	$123.45	$123.45	$123.50
7 purchase totals =	$547.28		$597.8095	$597.80	$597.85	$598.00