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	$77.93	5.795%	$82.446	$82.45	$82.45	$82.40
Purchase #2	$126.59	13.308%	$143.4366	$143.44	$143.45	$143.40
Purchase #3	$176.40	8.244%	$190.9424	$190.94	$190.95	$190.90
Purchase #4	$96.61	13.658%	$109.805	$109.81	$109.80	$109.80
Purchase #5	$77.73	13.208%	$87.9966	$88.00	$88.00	$88.00
Purchase #6	$172.30	13.787%	$196.055	$196.06	$196.05	$196.10
Purchase #7	$71.44	12.477%	$80.3536	$80.35	$80.35	$80.40
7 purchase totals =	$799.00		$891.0352	$891.05	$891.05	$891.00