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	$222.64	3.836%	$231.1805	$231.18	$231.20	$231.20
Purchase #2	$158.90	4.688%	$166.3492	$166.35	$166.35	$166.30
Purchase #3	$106.40	6.159%	$112.9532	$112.95	$112.95	$113.00
Purchase #4	$228.58	4.511%	$238.8912	$238.89	$238.90	$238.90
Purchase #5	$91.90	9.810%	$100.9154	$100.92	$100.90	$100.90
Purchase #6	$51.65	13.410%	$58.5763	$58.58	$58.60	$58.60
Purchase #7	$20.70	3.797%	$21.486	$21.49	$21.50	$21.50
7 purchase totals =	$880.77		$930.3518	$930.36	$930.40	$930.40