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	$248.81	7.797%	$268.2097	$268.21	$268.20	$268.20
Purchase #2	$11.94	5.474%	$12.5936	$12.59	$12.60	$12.60
Purchase #3	$74.32	11.471%	$82.8452	$82.85	$82.85	$82.80
Purchase #4	$178.79	4.393%	$186.6442	$186.64	$186.65	$186.60
Purchase #5	$38.37	4.650%	$40.1542	$40.15	$40.15	$40.20
Purchase #6	$90.32	10.114%	$99.455	$99.46	$99.45	$99.50
Purchase #7	$45.62	9.469%	$49.9398	$49.94	$49.95	$49.90
7 purchase totals =	$688.17		$739.8417	$739.84	$739.85	$739.80