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	$104.87	6.737%	$111.9351	$111.94	$111.95	$111.90
Purchase #2	$216.76	10.641%	$239.8254	$239.83	$239.85	$239.80
Purchase #3	$121.84	5.435%	$128.462	$128.46	$128.45	$128.50
Purchase #4	$203.68	11.396%	$226.8914	$226.89	$226.90	$226.90
Purchase #5	$119.37	10.106%	$131.4335	$131.43	$131.45	$131.40
Purchase #6	$242.38	11.671%	$270.6682	$270.67	$270.65	$270.70
Purchase #7	$29.63	9.811%	$32.537	$32.54	$32.55	$32.50
7 purchase totals =	$1,038.53		$1,141.7526	$1,141.76	$1,141.80	$1,141.70