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	$249.66	12.187%	$280.0861	$280.09	$280.10	$280.10
Purchase #2	$212.62	11.600%	$237.2839	$237.28	$237.30	$237.30
Purchase #3	$19.89	7.805%	$21.4424	$21.44	$21.45	$21.40
Purchase #4	$83.74	7.131%	$89.7115	$89.71	$89.70	$89.70
Purchase #5	$105.27	9.618%	$115.3949	$115.39	$115.40	$115.40
Purchase #6	$233.27	8.838%	$253.8864	$253.89	$253.90	$253.90
Purchase #7	$171.74	7.753%	$185.055	$185.06	$185.05	$185.10
7 purchase totals =	$1,076.19		$1,182.8602	$1,182.86	$1,182.90	$1,182.90