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	$100.72	11.775%	$112.5798	$112.58	$112.60	$112.60
Purchase #2	$244.65	10.512%	$270.3676	$270.37	$270.35	$270.40
Purchase #3	$231.43	10.410%	$255.5219	$255.52	$255.50	$255.50
Purchase #4	$160.54	8.784%	$174.6418	$174.64	$174.65	$174.60
Purchase #5	$48.96	11.338%	$54.5111	$54.51	$54.50	$54.50
Purchase #6	$89.30	12.791%	$100.7224	$100.72	$100.70	$100.70
Purchase #7	$63.47	4.839%	$66.5413	$66.54	$66.55	$66.50
7 purchase totals =	$939.07		$1,034.8859	$1,034.88	$1,034.85	$1,034.80