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	$88.98	13.206%	$100.7307	$100.73	$100.75	$100.70
Purchase #2	$58.51	13.792%	$66.5797	$66.58	$66.60	$66.60
Purchase #3	$56.37	13.237%	$63.8317	$63.83	$63.85	$63.80
Purchase #4	$216.38	11.851%	$242.0232	$242.02	$242.00	$242.00
Purchase #5	$11.61	12.399%	$13.0495	$13.05	$13.05	$13.00
Purchase #6	$242.76	5.579%	$256.3036	$256.30	$256.30	$256.30
Purchase #7	$217.73	3.730%	$225.8513	$225.85	$225.85	$225.90
7 purchase totals =	$892.34		$968.3697	$968.36	$968.40	$968.30