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	$173.31	5.362%	$182.6029	$182.60	$182.60	$182.60
Purchase #2	$123.26	11.539%	$137.483	$137.48	$137.50	$137.50
Purchase #3	$62.26	4.404%	$65.0019	$65.00	$65.00	$65.00
Purchase #4	$165.42	13.312%	$187.4407	$187.44	$187.45	$187.40
Purchase #5	$108.70	3.244%	$112.2262	$112.23	$112.25	$112.20
Purchase #6	$181.42	12.257%	$203.6566	$203.66	$203.65	$203.70
Purchase #7	$78.32	4.864%	$82.1295	$82.13	$82.15	$82.10
7 purchase totals =	$892.69		$970.5408	$970.54	$970.60	$970.50