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	$102.76	13.705%	$116.8433	$116.84	$116.85	$116.80
Purchase #2	$101.51	12.845%	$114.549	$114.55	$114.55	$114.50
Purchase #3	$245.83	3.834%	$255.2551	$255.26	$255.25	$255.30
Purchase #4	$59.35	4.246%	$61.87	$61.87	$61.85	$61.90
Purchase #5	$111.73	6.309%	$118.779	$118.78	$118.80	$118.80
Purchase #6	$5.73	8.473%	$6.2155	$6.22	$6.20	$6.20
Purchase #7	$92.32	6.478%	$98.3005	$98.30	$98.30	$98.30
7 purchase totals =	$719.23		$771.8124	$771.82	$771.80	$771.80