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	$99.56	4.783%	$104.322	$104.32	$104.30	$104.30
Purchase #2	$126.52	8.175%	$136.863	$136.86	$136.85	$136.90
Purchase #3	$21.78	13.236%	$24.6628	$24.66	$24.65	$24.70
Purchase #4	$99.45	10.213%	$109.6068	$109.61	$109.60	$109.60
Purchase #5	$34.46	5.794%	$36.4566	$36.46	$36.45	$36.50
Purchase #6	$63.50	3.203%	$65.5339	$65.53	$65.55	$65.50
Purchase #7	$142.73	8.108%	$154.3025	$154.30	$154.30	$154.30
7 purchase totals =	$588.00		$631.7476	$631.74	$631.70	$631.80