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	$37.79	13.193%	$42.7756	$42.78	$42.80	$42.80
Purchase #2	$215.59	9.542%	$236.1616	$236.16	$236.15	$236.20
Purchase #3	$158.89	13.395%	$180.1733	$180.17	$180.15	$180.20
Purchase #4	$169.75	9.183%	$185.3381	$185.34	$185.35	$185.30
Purchase #5	$190.49	13.147%	$215.5337	$215.53	$215.55	$215.50
Purchase #6	$14.28	9.342%	$15.614	$15.61	$15.60	$15.60
Purchase #7	$69.59	6.344%	$74.0048	$74.00	$74.00	$74.00
7 purchase totals =	$856.38		$949.6011	$949.59	$949.60	$949.60