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	$245.92	13.694%	$279.5963	$279.60	$279.60	$279.60
Purchase #2	$231.61	10.742%	$256.4895	$256.49	$256.50	$256.50
Purchase #3	$114.70	7.793%	$123.6386	$123.64	$123.65	$123.60
Purchase #4	$37.83	7.758%	$40.7649	$40.76	$40.75	$40.80
Purchase #5	$203.97	7.791%	$219.8613	$219.86	$219.85	$219.90
Purchase #6	$98.33	13.695%	$111.7963	$111.80	$111.80	$111.80
Purchase #7	$203.49	7.329%	$218.4038	$218.40	$218.40	$218.40
7 purchase totals =	$1,135.85		$1,250.5507	$1,250.55	$1,250.55	$1,250.60