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	$176.85	12.156%	$198.3479	$198.35	$198.35	$198.30
Purchase #2	$76.51	8.329%	$82.8825	$82.88	$82.90	$82.90
Purchase #3	$205.31	12.288%	$230.5385	$230.54	$230.55	$230.50
Purchase #4	$137.55	10.592%	$152.1193	$152.12	$152.10	$152.10
Purchase #5	$132.40	10.610%	$146.4476	$146.45	$146.45	$146.40
Purchase #6	$244.81	4.510%	$255.8509	$255.85	$255.85	$255.90
Purchase #7	$209.58	6.743%	$223.712	$223.71	$223.70	$223.70
7 purchase totals =	$1,183.01		$1,289.8987	$1,289.90	$1,289.90	$1,289.80