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	$19.99	5.624%	$21.1142	$21.11	$21.10	$21.10
Purchase #2	$69.43	10.639%	$76.8167	$76.82	$76.80	$76.80
Purchase #3	$105.92	4.849%	$111.0561	$111.06	$111.05	$111.10
Purchase #4	$219.41	12.474%	$246.7792	$246.78	$246.80	$246.80
Purchase #5	$179.82	11.462%	$200.431	$200.43	$200.45	$200.40
Purchase #6	$164.86	8.574%	$178.9951	$179.00	$179.00	$179.00
Purchase #7	$202.61	3.844%	$210.3983	$210.40	$210.40	$210.40
7 purchase totals =	$962.04		$1,045.5906	$1,045.60	$1,045.60	$1,045.60