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	$124.81	11.813%	$139.5538	$139.55	$139.55	$139.60
Purchase #2	$92.42	8.455%	$100.2341	$100.23	$100.25	$100.20
Purchase #3	$43.97	5.656%	$46.4569	$46.46	$46.45	$46.50
Purchase #4	$231.85	11.773%	$259.1457	$259.15	$259.15	$259.10
Purchase #5	$183.67	8.543%	$199.3609	$199.36	$199.35	$199.40
Purchase #6	$89.96	9.721%	$98.705	$98.71	$98.70	$98.70
Purchase #7	$127.87	4.576%	$133.7213	$133.72	$133.70	$133.70
7 purchase totals =	$894.55		$977.1777	$977.18	$977.15	$977.20