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	$143.75	10.327%	$158.5951	$158.60	$158.60	$158.60
Purchase #2	$65.75	11.406%	$73.2494	$73.25	$73.25	$73.20
Purchase #3	$24.69	4.578%	$25.8203	$25.82	$25.80	$25.80
Purchase #4	$143.81	13.248%	$162.8619	$162.86	$162.85	$162.90
Purchase #5	$17.63	6.147%	$18.7137	$18.71	$18.70	$18.70
Purchase #6	$200.87	3.556%	$208.0129	$208.01	$208.00	$208.00
Purchase #7	$155.32	3.357%	$160.5341	$160.53	$160.55	$160.50
7 purchase totals =	$751.82		$807.7874	$807.78	$807.75	$807.70