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	$21.90	12.367%	$24.6084	$24.61	$24.60	$24.60
Purchase #2	$37.93	4.290%	$39.5572	$39.56	$39.55	$39.60
Purchase #3	$119.39	5.563%	$126.0317	$126.03	$126.05	$126.00
Purchase #4	$81.63	11.117%	$90.7048	$90.70	$90.70	$90.70
Purchase #5	$213.47	12.592%	$240.3501	$240.35	$240.35	$240.40
Purchase #6	$20.50	10.794%	$22.7128	$22.71	$22.70	$22.70
Purchase #7	$222.70	12.663%	$250.9005	$250.90	$250.90	$250.90
7 purchase totals =	$717.52		$794.8655	$794.86	$794.85	$794.90