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	$242.86	11.232%	$270.138	$270.14	$270.15	$270.10
Purchase #2	$216.67	4.529%	$226.483	$226.48	$226.50	$226.50
Purchase #3	$119.68	10.292%	$131.9975	$132.00	$132.00	$132.00
Purchase #4	$179.35	3.551%	$185.7187	$185.72	$185.70	$185.70
Purchase #5	$218.50	12.710%	$246.2714	$246.27	$246.25	$246.30
Purchase #6	$31.71	5.335%	$33.4017	$33.40	$33.40	$33.40
Purchase #7	$69.89	3.671%	$72.4557	$72.46	$72.45	$72.50
7 purchase totals =	$1,078.66		$1,166.4660	$1,166.47	$1,166.45	$1,166.50