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	$148.61	13.286%	$168.3543	$168.35	$168.35	$168.40
Purchase #2	$51.60	4.523%	$53.9339	$53.93	$53.95	$53.90
Purchase #3	$191.71	12.380%	$215.4437	$215.44	$215.45	$215.40
Purchase #4	$35.53	12.121%	$39.8366	$39.84	$39.85	$39.80
Purchase #5	$83.39	13.531%	$94.6735	$94.67	$94.65	$94.70
Purchase #6	$247.80	10.626%	$274.1312	$274.13	$274.15	$274.10
Purchase #7	$15.88	13.385%	$18.0055	$18.01	$18.00	$18.00
7 purchase totals =	$774.52		$864.3787	$864.37	$864.40	$864.30