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	$199.71	4.319%	$208.3355	$208.34	$208.35	$208.30
Purchase #2	$183.86	6.470%	$195.7557	$195.76	$195.75	$195.80
Purchase #3	$82.99	7.569%	$89.2715	$89.27	$89.25	$89.30
Purchase #4	$160.34	13.123%	$181.3814	$181.38	$181.40	$181.40
Purchase #5	$169.55	13.851%	$193.0344	$193.03	$193.05	$193.00
Purchase #6	$112.77	6.475%	$120.0719	$120.07	$120.05	$120.10
Purchase #7	$103.78	7.855%	$111.9319	$111.93	$111.95	$111.90
7 purchase totals =	$1,013.00		$1,099.7823	$1,099.78	$1,099.80	$1,099.80