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	$48.30	13.557%	$54.848	$54.85	$54.85	$54.80
Purchase #2	$108.41	7.137%	$116.1472	$116.15	$116.15	$116.10
Purchase #3	$57.82	13.161%	$65.4297	$65.43	$65.45	$65.40
Purchase #4	$112.55	3.697%	$116.711	$116.71	$116.70	$116.70
Purchase #5	$66.68	8.172%	$72.1291	$72.13	$72.15	$72.10
Purchase #6	$86.34	6.246%	$91.7328	$91.73	$91.75	$91.70
Purchase #7	$112.81	6.282%	$119.8967	$119.90	$119.90	$119.90
7 purchase totals =	$592.91		$636.8945	$636.90	$636.95	$636.70