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	$241.80	13.731%	$275.0016	$275.00	$275.00	$275.00
Purchase #2	$247.91	13.294%	$280.8672	$280.87	$280.85	$280.90
Purchase #3	$236.46	4.788%	$247.7817	$247.78	$247.80	$247.80
Purchase #4	$227.31	6.156%	$241.3032	$241.30	$241.30	$241.30
Purchase #5	$174.99	12.237%	$196.4035	$196.40	$196.40	$196.40
Purchase #6	$17.74	13.812%	$20.1902	$20.19	$20.20	$20.20
Purchase #7	$219.92	4.337%	$229.4579	$229.46	$229.45	$229.50
7 purchase totals =	$1,366.13		$1,491.0053	$1,491.00	$1,491.00	$1,491.10