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	$124.59	12.856%	$140.6073	$140.61	$140.60	$140.60
Purchase #2	$230.43	8.177%	$249.2723	$249.27	$249.25	$249.30
Purchase #3	$98.59	6.490%	$104.9885	$104.99	$105.00	$105.00
Purchase #4	$136.97	5.347%	$144.2938	$144.29	$144.30	$144.30
Purchase #5	$92.88	7.149%	$99.52	$99.52	$99.50	$99.50
Purchase #6	$241.64	13.339%	$273.8724	$273.87	$273.85	$273.90
Purchase #7	$185.98	13.774%	$211.5969	$211.60	$211.60	$211.60
7 purchase totals =	$1,111.08		$1,224.1512	$1,224.15	$1,224.10	$1,224.20