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	$185.93	13.377%	$210.8019	$210.80	$210.80	$210.80
Purchase #2	$178.47	9.517%	$195.455	$195.46	$195.45	$195.50
Purchase #3	$165.68	5.381%	$174.5952	$174.60	$174.60	$174.60
Purchase #4	$216.38	11.585%	$241.4476	$241.45	$241.45	$241.40
Purchase #5	$200.97	8.371%	$217.7932	$217.79	$217.80	$217.80
Purchase #6	$240.89	4.149%	$250.8845	$250.88	$250.90	$250.90
Purchase #7	$88.61	13.408%	$100.4908	$100.49	$100.50	$100.50
7 purchase totals =	$1,276.93		$1,391.4682	$1,391.47	$1,391.50	$1,391.50