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	$54.82	12.197%	$61.5064	$61.51	$61.50	$61.50
Purchase #2	$123.90	12.861%	$139.8348	$139.83	$139.85	$139.80
Purchase #3	$154.42	7.685%	$166.2872	$166.29	$166.30	$166.30
Purchase #4	$73.56	10.639%	$81.386	$81.39	$81.40	$81.40
Purchase #5	$165.67	9.622%	$181.6108	$181.61	$181.60	$181.60
Purchase #6	$235.36	3.164%	$242.8068	$242.81	$242.80	$242.80
Purchase #7	$118.50	12.521%	$133.3374	$133.34	$133.35	$133.30
7 purchase totals =	$926.23		$1,006.7694	$1,006.78	$1,006.80	$1,006.70