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	$145.90	13.659%	$165.8285	$165.83	$165.85	$165.80
Purchase #2	$248.27	3.204%	$256.2246	$256.22	$256.20	$256.20
Purchase #3	$132.75	12.185%	$148.9256	$148.93	$148.95	$148.90
Purchase #4	$139.80	4.403%	$145.9554	$145.96	$145.95	$146.00
Purchase #5	$170.90	8.387%	$185.2334	$185.23	$185.25	$185.20
Purchase #6	$110.96	4.350%	$115.7868	$115.79	$115.80	$115.80
Purchase #7	$94.97	11.548%	$105.9371	$105.94	$105.95	$105.90
7 purchase totals =	$1,043.55		$1,123.8914	$1,123.90	$1,123.95	$1,123.80