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	$218.29	9.667%	$239.3921	$239.39	$239.40	$239.40
Purchase #2	$221.80	3.296%	$229.1105	$229.11	$229.10	$229.10
Purchase #3	$121.49	13.203%	$137.5303	$137.53	$137.55	$137.50
Purchase #4	$74.48	10.774%	$82.5045	$82.50	$82.50	$82.50
Purchase #5	$187.28	4.787%	$196.2451	$196.25	$196.25	$196.20
Purchase #6	$239.87	13.150%	$271.4129	$271.41	$271.40	$271.40
Purchase #7	$108.35	3.642%	$112.2961	$112.30	$112.30	$112.30
7 purchase totals =	$1,171.56		$1,268.4915	$1,268.49	$1,268.50	$1,268.40