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	$218.28	13.566%	$247.8919	$247.89	$247.90	$247.90
Purchase #2	$136.43	10.322%	$150.5123	$150.51	$150.50	$150.50
Purchase #3	$215.78	11.548%	$240.6983	$240.70	$240.70	$240.70
Purchase #4	$45.76	7.856%	$49.3549	$49.35	$49.35	$49.40
Purchase #5	$130.32	3.242%	$134.545	$134.55	$134.55	$134.50
Purchase #6	$38.61	12.513%	$43.4413	$43.44	$43.45	$43.40
Purchase #7	$80.96	11.352%	$90.1506	$90.15	$90.15	$90.20
7 purchase totals =	$866.14		$956.5943	$956.59	$956.60	$956.60