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	$120.52	13.441%	$136.7191	$136.72	$136.70	$136.70
Purchase #2	$193.81	8.280%	$209.8575	$209.86	$209.85	$209.90
Purchase #3	$125.39	11.221%	$139.46	$139.46	$139.45	$139.50
Purchase #4	$146.66	12.248%	$164.6229	$164.62	$164.60	$164.60
Purchase #5	$54.56	3.859%	$56.6655	$56.67	$56.65	$56.70
Purchase #6	$70.82	12.558%	$79.7136	$79.71	$79.70	$79.70
Purchase #7	$117.72	5.168%	$123.8038	$123.80	$123.80	$123.80
7 purchase totals =	$829.48		$910.8424	$910.84	$910.75	$910.90