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	$231.52	10.841%	$256.6191	$256.62	$256.60	$256.60
Purchase #2	$97.70	7.584%	$105.1096	$105.11	$105.10	$105.10
Purchase #3	$218.43	12.392%	$245.4978	$245.50	$245.50	$245.50
Purchase #4	$20.28	5.800%	$21.4562	$21.46	$21.45	$21.50
Purchase #5	$50.34	13.597%	$57.1847	$57.18	$57.20	$57.20
Purchase #6	$88.28	7.189%	$94.6264	$94.63	$94.65	$94.60
Purchase #7	$211.92	6.305%	$225.2816	$225.28	$225.30	$225.30
7 purchase totals =	$918.47		$1,005.7754	$1,005.78	$1,005.80	$1,005.80