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	$247.78	13.317%	$280.7769	$280.78	$280.80	$280.80
Purchase #2	$52.67	11.469%	$58.7107	$58.71	$58.70	$58.70
Purchase #3	$31.36	5.712%	$33.1513	$33.15	$33.15	$33.20
Purchase #4	$83.81	6.194%	$89.0012	$89.00	$89.00	$89.00
Purchase #5	$141.67	10.478%	$156.5142	$156.51	$156.50	$156.50
Purchase #6	$29.77	9.764%	$32.6767	$32.68	$32.70	$32.70
Purchase #7	$108.60	9.106%	$118.4891	$118.49	$118.50	$118.50
7 purchase totals =	$695.66		$769.3201	$769.32	$769.35	$769.40