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	$74.42	5.240%	$78.3196	$78.32	$78.30	$78.30
Purchase #2	$174.59	8.625%	$189.6484	$189.65	$189.65	$189.60
Purchase #3	$5.45	11.819%	$6.0941	$6.09	$6.10	$6.10
Purchase #4	$64.27	4.818%	$67.3665	$67.37	$67.35	$67.40
Purchase #5	$249.97	12.327%	$280.7838	$280.78	$280.80	$280.80
Purchase #6	$121.92	4.858%	$127.8429	$127.84	$127.85	$127.80
Purchase #7	$248.77	13.256%	$281.747	$281.75	$281.75	$281.70
7 purchase totals =	$939.39		$1,031.8023	$1,031.80	$1,031.80	$1,031.70