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	$140.72	6.542%	$149.9259	$149.93	$149.95	$149.90
Purchase #2	$110.59	3.639%	$114.6144	$114.61	$114.60	$114.60
Purchase #3	$142.79	10.747%	$158.1356	$158.14	$158.15	$158.10
Purchase #4	$80.41	6.788%	$85.8682	$85.87	$85.85	$85.90
Purchase #5	$110.78	9.175%	$120.9441	$120.94	$120.95	$120.90
Purchase #6	$33.51	10.517%	$37.0342	$37.03	$37.05	$37.00
Purchase #7	$65.98	4.674%	$69.0639	$69.06	$69.05	$69.10
7 purchase totals =	$684.78		$735.5863	$735.58	$735.60	$735.50