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	$62.54	7.870%	$67.4619	$67.46	$67.45	$67.50
Purchase #2	$248.90	13.214%	$281.7896	$281.79	$281.80	$281.80
Purchase #3	$199.25	5.292%	$209.7943	$209.79	$209.80	$209.80
Purchase #4	$174.37	9.853%	$191.5507	$191.55	$191.55	$191.60
Purchase #5	$143.62	10.321%	$158.443	$158.44	$158.45	$158.40
Purchase #6	$59.42	5.859%	$62.9014	$62.90	$62.90	$62.90
Purchase #7	$22.94	11.837%	$25.6554	$25.66	$25.65	$25.70
7 purchase totals =	$911.04		$997.5963	$997.59	$997.60	$997.70