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	$239.48	8.172%	$259.0503	$259.05	$259.05	$259.10
Purchase #2	$240.73	6.406%	$256.1512	$256.15	$256.15	$256.20
Purchase #3	$43.88	6.383%	$46.6809	$46.68	$46.70	$46.70
Purchase #4	$131.59	10.660%	$145.6175	$145.62	$145.60	$145.60
Purchase #5	$250.50	7.505%	$269.3	$269.30	$269.30	$269.30
Purchase #6	$79.98	11.868%	$89.472	$89.47	$89.45	$89.50
Purchase #7	$245.93	9.623%	$269.5958	$269.60	$269.60	$269.60
7 purchase totals =	$1,232.09		$1,335.8677	$1,335.87	$1,335.85	$1,336.00