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	$250.89	13.657%	$285.154	$285.15	$285.15	$285.20
Purchase #2	$138.38	13.135%	$156.5562	$156.56	$156.55	$156.60
Purchase #3	$75.46	4.533%	$78.8806	$78.88	$78.90	$78.90
Purchase #4	$233.90	5.163%	$245.9763	$245.98	$246.00	$246.00
Purchase #5	$64.45	6.451%	$68.6077	$68.61	$68.60	$68.60
Purchase #6	$77.82	13.462%	$88.2961	$88.30	$88.30	$88.30
Purchase #7	$128.27	10.517%	$141.7602	$141.76	$141.75	$141.80
7 purchase totals =	$969.17		$1,065.2311	$1,065.24	$1,065.25	$1,065.40