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	$12.81	4.236%	$13.3526	$13.35	$13.35	$13.40
Purchase #2	$132.78	9.129%	$144.9015	$144.90	$144.90	$144.90
Purchase #3	$151.50	12.370%	$170.2406	$170.24	$170.25	$170.20
Purchase #4	$65.55	8.173%	$70.9074	$70.91	$70.90	$70.90
Purchase #5	$242.89	5.730%	$256.8076	$256.81	$256.80	$256.80
Purchase #6	$180.75	6.120%	$191.8119	$191.81	$191.80	$191.80
Purchase #7	$164.28	3.806%	$170.5325	$170.53	$170.55	$170.50
7 purchase totals =	$950.56		$1,018.5541	$1,018.55	$1,018.55	$1,018.50