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	$248.44	9.668%	$272.4592	$272.46	$272.45	$272.50
Purchase #2	$99.59	4.830%	$104.4002	$104.40	$104.40	$104.40
Purchase #3	$117.42	13.651%	$133.449	$133.45	$133.45	$133.40
Purchase #4	$246.31	12.602%	$277.35	$277.35	$277.35	$277.40
Purchase #5	$55.43	8.194%	$59.9719	$59.97	$59.95	$60.00
Purchase #6	$177.52	6.166%	$188.4659	$188.47	$188.45	$188.50
Purchase #7	$47.62	12.127%	$53.3949	$53.39	$53.40	$53.40
7 purchase totals =	$992.33		$1,089.4911	$1,089.49	$1,089.45	$1,089.60