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	$39.31	8.257%	$42.5558	$42.56	$42.55	$42.60
Purchase #2	$218.38	7.509%	$234.7782	$234.78	$234.80	$234.80
Purchase #3	$99.39	10.296%	$109.6232	$109.62	$109.60	$109.60
Purchase #4	$103.33	5.226%	$108.73	$108.73	$108.75	$108.70
Purchase #5	$122.47	6.652%	$130.6167	$130.62	$130.60	$130.60
Purchase #6	$38.42	5.355%	$40.4774	$40.48	$40.50	$40.50
Purchase #7	$65.66	4.279%	$68.4696	$68.47	$68.45	$68.50
7 purchase totals =	$686.96		$735.2509	$735.26	$735.25	$735.30