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	$60.80	8.684%	$66.0799	$66.08	$66.10	$66.10
Purchase #2	$94.38	9.721%	$103.5547	$103.55	$103.55	$103.60
Purchase #3	$244.93	10.346%	$270.2705	$270.27	$270.25	$270.30
Purchase #4	$176.64	8.244%	$191.2022	$191.20	$191.20	$191.20
Purchase #5	$138.35	9.246%	$151.1418	$151.14	$151.15	$151.10
Purchase #6	$136.72	3.760%	$141.8607	$141.86	$141.85	$141.90
Purchase #7	$54.74	9.148%	$59.7476	$59.75	$59.75	$59.70
7 purchase totals =	$906.56		$983.8574	$983.85	$983.85	$983.90