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	$175.65	9.583%	$192.4825	$192.48	$192.50	$192.50
Purchase #2	$248.45	8.337%	$269.1633	$269.16	$269.15	$269.20
Purchase #3	$143.77	10.740%	$159.2109	$159.21	$159.20	$159.20
Purchase #4	$118.95	12.295%	$133.5749	$133.57	$133.55	$133.60
Purchase #5	$184.88	6.481%	$196.8621	$196.86	$196.85	$196.90
Purchase #6	$233.61	8.537%	$253.5533	$253.55	$253.55	$253.60
Purchase #7	$177.35	4.569%	$185.4531	$185.45	$185.45	$185.50
7 purchase totals =	$1,282.66		$1,390.3001	$1,390.28	$1,390.25	$1,390.50