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	$158.94	8.777%	$172.8902	$172.89	$172.90	$172.90
Purchase #2	$207.30	12.795%	$233.824	$233.82	$233.80	$233.80
Purchase #3	$137.51	9.339%	$150.3521	$150.35	$150.35	$150.40
Purchase #4	$114.39	10.262%	$126.1287	$126.13	$126.15	$126.10
Purchase #5	$36.63	11.330%	$40.7802	$40.78	$40.80	$40.80
Purchase #6	$111.81	12.725%	$126.0378	$126.04	$126.05	$126.00
Purchase #7	$73.86	8.515%	$80.1492	$80.15	$80.15	$80.10
7 purchase totals =	$840.44		$930.1622	$930.16	$930.20	$930.10