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	$136.27	12.184%	$152.8731	$152.87	$152.85	$152.90
Purchase #2	$57.87	12.466%	$65.0841	$65.08	$65.10	$65.10
Purchase #3	$224.48	3.106%	$231.4523	$231.45	$231.45	$231.50
Purchase #4	$155.27	3.377%	$160.5135	$160.51	$160.50	$160.50
Purchase #5	$33.76	13.386%	$38.2791	$38.28	$38.30	$38.30
Purchase #6	$38.77	6.724%	$41.3769	$41.38	$41.40	$41.40
Purchase #7	$109.30	9.714%	$119.9174	$119.92	$119.90	$119.90
7 purchase totals =	$755.72		$809.4964	$809.49	$809.50	$809.60