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	$246.35	12.659%	$277.5354	$277.54	$277.55	$277.50
Purchase #2	$84.60	7.390%	$90.8519	$90.85	$90.85	$90.90
Purchase #3	$176.65	13.249%	$200.0544	$200.05	$200.05	$200.10
Purchase #4	$39.58	9.725%	$43.4292	$43.43	$43.45	$43.40
Purchase #5	$88.46	9.184%	$96.5842	$96.58	$96.60	$96.60
Purchase #6	$124.37	13.706%	$141.4162	$141.42	$141.40	$141.40
Purchase #7	$44.25	11.262%	$49.2334	$49.23	$49.25	$49.20
7 purchase totals =	$804.26		$899.1047	$899.10	$899.15	$899.10