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	$27.86	13.614%	$31.6529	$31.65	$31.65	$31.70
Purchase #2	$155.84	12.478%	$175.2857	$175.29	$175.30	$175.30
Purchase #3	$207.94	6.251%	$220.9383	$220.94	$220.95	$220.90
Purchase #4	$68.98	13.462%	$78.2661	$78.27	$78.25	$78.30
Purchase #5	$46.71	12.612%	$52.6011	$52.60	$52.60	$52.60
Purchase #6	$82.58	5.151%	$86.8337	$86.83	$86.85	$86.80
Purchase #7	$117.35	13.287%	$132.9423	$132.94	$132.95	$132.90
7 purchase totals =	$707.26		$778.5201	$778.52	$778.55	$778.50