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	$79.46	12.366%	$89.286	$89.29	$89.30	$89.30
Purchase #2	$247.80	7.660%	$266.7815	$266.78	$266.80	$266.80
Purchase #3	$120.94	12.699%	$136.2982	$136.30	$136.30	$136.30
Purchase #4	$132.50	5.752%	$140.1214	$140.12	$140.10	$140.10
Purchase #5	$231.78	4.506%	$242.224	$242.22	$242.20	$242.20
Purchase #6	$42.49	11.788%	$47.4987	$47.50	$47.50	$47.50
Purchase #7	$163.39	11.151%	$181.6096	$181.61	$181.60	$181.60
7 purchase totals =	$1,018.36		$1,103.8194	$1,103.82	$1,103.80	$1,103.80