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	$222.68	11.645%	$248.6111	$248.61	$248.60	$248.60
Purchase #2	$92.31	11.236%	$102.682	$102.68	$102.70	$102.70
Purchase #3	$21.37	5.598%	$22.5663	$22.57	$22.55	$22.60
Purchase #4	$104.63	6.535%	$111.4676	$111.47	$111.45	$111.50
Purchase #5	$103.65	12.204%	$116.2994	$116.30	$116.30	$116.30
Purchase #6	$146.82	10.385%	$162.0673	$162.07	$162.05	$162.10
Purchase #7	$51.65	9.671%	$56.6451	$56.65	$56.65	$56.60
7 purchase totals =	$743.11		$820.3388	$820.35	$820.30	$820.40