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	$213.75	3.525%	$221.2847	$221.28	$221.30	$221.30
Purchase #2	$127.78	9.760%	$140.2513	$140.25	$140.25	$140.30
Purchase #3	$236.49	8.169%	$255.8089	$255.81	$255.80	$255.80
Purchase #4	$96.48	11.819%	$107.883	$107.88	$107.90	$107.90
Purchase #5	$25.85	4.814%	$27.0944	$27.09	$27.10	$27.10
Purchase #6	$137.39	5.417%	$144.8324	$144.83	$144.85	$144.80
Purchase #7	$90.75	12.560%	$102.1482	$102.15	$102.15	$102.10
7 purchase totals =	$928.49		$999.3029	$999.29	$999.35	$999.30