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	$127.82	9.228%	$139.6152	$139.62	$139.60	$139.60
Purchase #2	$78.51	13.261%	$88.9212	$88.92	$88.90	$88.90
Purchase #3	$143.64	5.669%	$151.783	$151.78	$151.80	$151.80
Purchase #4	$82.33	8.517%	$89.342	$89.34	$89.35	$89.30
Purchase #5	$108.84	13.512%	$123.5465	$123.55	$123.55	$123.50
Purchase #6	$237.98	8.420%	$258.0179	$258.02	$258.00	$258.00
Purchase #7	$180.77	10.780%	$200.257	$200.26	$200.25	$200.30
7 purchase totals =	$959.89		$1,051.4828	$1,051.49	$1,051.45	$1,051.40