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	$220.70	4.814%	$231.3245	$231.32	$231.30	$231.30
Purchase #2	$59.39	11.851%	$66.4283	$66.43	$66.45	$66.40
Purchase #3	$52.38	9.601%	$57.409	$57.41	$57.40	$57.40
Purchase #4	$216.69	11.621%	$241.8715	$241.87	$241.85	$241.90
Purchase #5	$166.37	11.473%	$185.4576	$185.46	$185.45	$185.50
Purchase #6	$219.65	5.171%	$231.0081	$231.01	$231.00	$231.00
Purchase #7	$121.97	8.230%	$132.0081	$132.01	$132.00	$132.00
7 purchase totals =	$1,057.15		$1,145.5071	$1,145.51	$1,145.45	$1,145.50