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	$75.27	5.580%	$79.4701	$79.47	$79.45	$79.50
Purchase #2	$84.26	13.527%	$95.6579	$95.66	$95.65	$95.70
Purchase #3	$26.74	10.715%	$29.6052	$29.61	$29.60	$29.60
Purchase #4	$43.27	7.114%	$46.3482	$46.35	$46.35	$46.30
Purchase #5	$103.58	13.508%	$117.5716	$117.57	$117.55	$117.60
Purchase #6	$80.56	10.787%	$89.25	$89.25	$89.25	$89.30
Purchase #7	$246.33	13.780%	$280.2743	$280.27	$280.25	$280.30
7 purchase totals =	$660.01		$738.1773	$738.18	$738.10	$738.30