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	$33.68	4.182%	$35.0885	$35.09	$35.10	$35.10
Purchase #2	$224.30	10.794%	$248.5109	$248.51	$248.50	$248.50
Purchase #3	$29.94	12.280%	$33.6166	$33.62	$33.60	$33.60
Purchase #4	$22.78	7.328%	$24.4493	$24.45	$24.45	$24.40
Purchase #5	$52.34	4.361%	$54.6225	$54.62	$54.60	$54.60
Purchase #6	$115.85	13.306%	$131.265	$131.27	$131.25	$131.30
Purchase #7	$93.37	8.684%	$101.4783	$101.48	$101.50	$101.50
7 purchase totals =	$572.26		$629.0311	$629.04	$629.00	$629.00