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	$108.54	3.596%	$112.4431	$112.44	$112.45	$112.40
Purchase #2	$54.87	9.841%	$60.2698	$60.27	$60.25	$60.30
Purchase #3	$107.39	3.856%	$111.531	$111.53	$111.55	$111.50
Purchase #4	$211.35	5.835%	$223.6823	$223.68	$223.70	$223.70
Purchase #5	$223.68	13.340%	$253.5189	$253.52	$253.50	$253.50
Purchase #6	$117.93	8.569%	$128.0354	$128.04	$128.05	$128.00
Purchase #7	$81.30	7.482%	$87.3829	$87.38	$87.40	$87.40
7 purchase totals =	$905.06		$976.8634	$976.86	$976.90	$976.80