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	$82.58	9.692%	$90.5837	$90.58	$90.60	$90.60
Purchase #2	$28.58	13.778%	$32.5178	$32.52	$32.50	$32.50
Purchase #3	$17.67	13.716%	$20.0936	$20.09	$20.10	$20.10
Purchase #4	$79.46	4.337%	$82.9062	$82.91	$82.90	$82.90
Purchase #5	$240.55	13.480%	$272.9761	$272.98	$273.00	$273.00
Purchase #6	$160.80	9.594%	$176.2272	$176.23	$176.25	$176.20
Purchase #7	$141.81	6.208%	$150.6136	$150.61	$150.60	$150.60
7 purchase totals =	$751.45		$825.9182	$825.92	$825.95	$825.90