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	$37.61	12.255%	$42.2191	$42.22	$42.20	$42.20
Purchase #2	$42.34	10.530%	$46.7984	$46.80	$46.80	$46.80
Purchase #3	$208.96	11.314%	$232.6017	$232.60	$232.60	$232.60
Purchase #4	$40.85	4.725%	$42.7802	$42.78	$42.80	$42.80
Purchase #5	$200.55	6.639%	$213.8645	$213.86	$213.85	$213.90
Purchase #6	$46.75	8.606%	$50.7733	$50.77	$50.75	$50.80
Purchase #7	$133.70	8.639%	$145.2503	$145.25	$145.25	$145.30
7 purchase totals =	$710.76		$774.2875	$774.28	$774.25	$774.40