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	$124.74	5.462%	$131.5533	$131.55	$131.55	$131.60
Purchase #2	$34.57	12.594%	$38.9237	$38.92	$38.90	$38.90
Purchase #3	$137.43	8.215%	$148.7199	$148.72	$148.70	$148.70
Purchase #4	$11.26	10.597%	$12.4532	$12.45	$12.45	$12.50
Purchase #5	$68.81	5.241%	$72.4163	$72.42	$72.40	$72.40
Purchase #6	$196.25	7.602%	$211.1689	$211.17	$211.15	$211.20
Purchase #7	$238.29	13.696%	$270.9262	$270.93	$270.95	$270.90
7 purchase totals =	$811.35		$886.1615	$886.16	$886.10	$886.20