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	$19.43	5.398%	$20.4788	$20.48	$20.50	$20.50
Purchase #2	$98.46	7.638%	$105.9804	$105.98	$106.00	$106.00
Purchase #3	$112.85	4.789%	$118.2544	$118.25	$118.25	$118.30
Purchase #4	$36.50	10.384%	$40.2902	$40.29	$40.30	$40.30
Purchase #5	$112.45	7.176%	$120.5194	$120.52	$120.50	$120.50
Purchase #6	$190.56	8.558%	$206.8681	$206.87	$206.85	$206.90
Purchase #7	$235.63	9.831%	$258.7948	$258.79	$258.80	$258.80
7 purchase totals =	$805.88		$871.1861	$871.18	$871.20	$871.30