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	$85.26	4.829%	$89.3772	$89.38	$89.40	$89.40
Purchase #2	$160.51	4.577%	$167.8565	$167.86	$167.85	$167.90
Purchase #3	$70.61	11.649%	$78.8354	$78.84	$78.85	$78.80
Purchase #4	$236.94	12.453%	$266.4461	$266.45	$266.45	$266.40
Purchase #5	$81.74	5.789%	$86.4719	$86.47	$86.45	$86.50
Purchase #6	$218.78	9.264%	$239.0478	$239.05	$239.05	$239.00
Purchase #7	$124.31	13.273%	$140.8097	$140.81	$140.80	$140.80
7 purchase totals =	$978.15		$1,068.8446	$1,068.86	$1,068.85	$1,068.80