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	$103.88	8.383%	$112.5883	$112.59	$112.60	$112.60
Purchase #2	$22.52	9.700%	$24.7044	$24.70	$24.70	$24.70
Purchase #3	$104.38	4.864%	$109.457	$109.46	$109.45	$109.50
Purchase #4	$23.51	12.245%	$26.3888	$26.39	$26.40	$26.40
Purchase #5	$158.90	5.388%	$167.4615	$167.46	$167.45	$167.50
Purchase #6	$50.72	7.664%	$54.6072	$54.61	$54.60	$54.60
Purchase #7	$88.85	6.672%	$94.7781	$94.78	$94.80	$94.80
7 purchase totals =	$552.76		$589.9853	$589.99	$590.00	$590.10