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	$29.29	12.443%	$32.9346	$32.93	$32.95	$32.90
Purchase #2	$231.51	9.485%	$253.4687	$253.47	$253.45	$253.50
Purchase #3	$186.27	9.853%	$204.6232	$204.62	$204.60	$204.60
Purchase #4	$195.98	12.165%	$219.821	$219.82	$219.80	$219.80
Purchase #5	$107.52	3.661%	$111.4563	$111.46	$111.45	$111.50
Purchase #6	$140.38	3.217%	$144.896	$144.90	$144.90	$144.90
Purchase #7	$119.51	13.749%	$135.9414	$135.94	$135.95	$135.90
7 purchase totals =	$1,010.46		$1,103.1412	$1,103.14	$1,103.10	$1,103.10