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	$246.41	13.817%	$280.4565	$280.46	$280.45	$280.50
Purchase #2	$112.43	10.664%	$124.4195	$124.42	$124.40	$124.40
Purchase #3	$212.59	13.619%	$241.5426	$241.54	$241.55	$241.50
Purchase #4	$249.26	12.680%	$280.8662	$280.87	$280.85	$280.90
Purchase #5	$65.34	9.542%	$71.5747	$71.57	$71.55	$71.60
Purchase #6	$211.28	10.797%	$234.0919	$234.09	$234.10	$234.10
Purchase #7	$79.33	7.568%	$85.3337	$85.33	$85.35	$85.30
7 purchase totals =	$1,176.64		$1,318.2851	$1,318.28	$1,318.25	$1,318.30