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	$247.40	5.460%	$260.908	$260.91	$260.90	$260.90
Purchase #2	$11.75	8.806%	$12.7847	$12.78	$12.80	$12.80
Purchase #3	$6.93	3.154%	$7.1486	$7.15	$7.15	$7.10
Purchase #4	$80.74	5.443%	$85.1347	$85.13	$85.15	$85.10
Purchase #5	$75.30	4.785%	$78.9031	$78.90	$78.90	$78.90
Purchase #6	$137.79	12.291%	$154.7258	$154.73	$154.75	$154.70
Purchase #7	$37.25	9.622%	$40.8342	$40.83	$40.85	$40.80
7 purchase totals =	$597.16		$640.4391	$640.43	$640.50	$640.30