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	$81.60	13.417%	$92.5483	$92.55	$92.55	$92.50
Purchase #2	$86.65	3.679%	$89.8379	$89.84	$89.85	$89.80
Purchase #3	$80.79	9.628%	$88.5685	$88.57	$88.55	$88.60
Purchase #4	$158.96	10.433%	$175.5443	$175.54	$175.55	$175.50
Purchase #5	$127.52	12.350%	$143.2687	$143.27	$143.25	$143.30
Purchase #6	$159.78	9.120%	$174.3519	$174.35	$174.35	$174.40
Purchase #7	$124.93	13.306%	$141.5532	$141.55	$141.55	$141.60
7 purchase totals =	$820.23		$905.6728	$905.67	$905.65	$905.70