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	$43.40	4.584%	$45.3895	$45.39	$45.40	$45.40
Purchase #2	$100.90	12.673%	$113.6871	$113.69	$113.70	$113.70
Purchase #3	$190.95	6.447%	$203.2605	$203.26	$203.25	$203.30
Purchase #4	$47.29	12.384%	$53.1464	$53.15	$53.15	$53.10
Purchase #5	$80.58	12.335%	$90.5195	$90.52	$90.50	$90.50
Purchase #6	$137.54	11.641%	$153.551	$153.55	$153.55	$153.60
Purchase #7	$246.35	8.662%	$267.6888	$267.69	$267.70	$267.70
7 purchase totals =	$847.01		$927.2428	$927.25	$927.25	$927.30