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	$78.58	5.211%	$82.6748	$82.67	$82.65	$82.70
Purchase #2	$38.53	12.684%	$43.4171	$43.42	$43.40	$43.40
Purchase #3	$38.92	4.300%	$40.5936	$40.59	$40.60	$40.60
Purchase #4	$31.98	12.299%	$35.9132	$35.91	$35.90	$35.90
Purchase #5	$31.28	10.187%	$34.4665	$34.47	$34.45	$34.50
Purchase #6	$133.26	13.335%	$151.0302	$151.03	$151.05	$151.00
Purchase #7	$158.60	11.566%	$176.9437	$176.94	$176.95	$176.90
7 purchase totals =	$511.15		$565.0391	$565.03	$565.00	$565.00