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	$238.63	4.256%	$248.7861	$248.79	$248.80	$248.80
Purchase #2	$96.65	8.468%	$104.8343	$104.83	$104.85	$104.80
Purchase #3	$100.63	8.147%	$108.8283	$108.83	$108.85	$108.80
Purchase #4	$99.51	5.742%	$105.2239	$105.22	$105.20	$105.20
Purchase #5	$56.36	8.804%	$61.3219	$61.32	$61.30	$61.30
Purchase #6	$26.62	12.659%	$29.9898	$29.99	$30.00	$30.00
Purchase #7	$73.83	13.221%	$83.5911	$83.59	$83.60	$83.60
7 purchase totals =	$692.23		$742.5754	$742.57	$742.60	$742.50