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	$134.55	5.729%	$142.2584	$142.26	$142.25	$142.30
Purchase #2	$118.86	7.492%	$127.765	$127.77	$127.75	$127.80
Purchase #3	$166.37	11.849%	$186.0832	$186.08	$186.10	$186.10
Purchase #4	$29.93	13.357%	$33.9278	$33.93	$33.95	$33.90
Purchase #5	$125.46	10.839%	$139.0586	$139.06	$139.05	$139.10
Purchase #6	$30.93	6.684%	$32.9974	$33.00	$33.00	$33.00
Purchase #7	$78.35	3.696%	$81.2458	$81.25	$81.25	$81.20
7 purchase totals =	$684.45		$743.3362	$743.35	$743.35	$743.40