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	$166.61	3.125%	$171.8166	$171.82	$171.80	$171.80
Purchase #2	$29.88	6.802%	$31.9124	$31.91	$31.90	$31.90
Purchase #3	$111.39	4.426%	$116.3201	$116.32	$116.30	$116.30
Purchase #4	$249.70	9.294%	$272.9071	$272.91	$272.90	$272.90
Purchase #5	$89.34	13.568%	$101.4617	$101.46	$101.45	$101.50
Purchase #6	$48.50	5.190%	$51.0172	$51.02	$51.00	$51.00
Purchase #7	$233.85	11.347%	$260.385	$260.39	$260.40	$260.40
7 purchase totals =	$929.27		$1,005.8201	$1,005.83	$1,005.75	$1,005.80