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	$75.34	4.538%	$78.7589	$78.76	$78.75	$78.80
Purchase #2	$129.84	8.183%	$140.4648	$140.46	$140.45	$140.50
Purchase #3	$136.49	10.340%	$150.6031	$150.60	$150.60	$150.60
Purchase #4	$76.32	13.201%	$86.395	$86.40	$86.40	$86.40
Purchase #5	$142.35	10.246%	$156.9352	$156.94	$156.95	$156.90
Purchase #6	$11.57	10.585%	$12.7947	$12.79	$12.80	$12.80
Purchase #7	$22.64	6.329%	$24.0729	$24.07	$24.05	$24.10
7 purchase totals =	$594.55		$650.0246	$650.02	$650.00	$650.10