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	$226.76	12.730%	$255.6265	$255.63	$255.65	$255.60
Purchase #2	$75.92	8.568%	$82.4248	$82.42	$82.40	$82.40
Purchase #3	$214.49	4.471%	$224.0798	$224.08	$224.10	$224.10
Purchase #4	$240.72	12.357%	$270.4658	$270.47	$270.45	$270.50
Purchase #5	$75.43	9.338%	$82.4737	$82.47	$82.45	$82.50
Purchase #6	$54.90	12.228%	$61.6132	$61.61	$61.60	$61.60
Purchase #7	$240.89	10.603%	$266.4316	$266.43	$266.45	$266.40
7 purchase totals =	$1,129.11		$1,243.1154	$1,243.11	$1,243.10	$1,243.10