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	$42.55	4.611%	$44.512	$44.51	$44.50	$44.50
Purchase #2	$179.30	4.818%	$187.9387	$187.94	$187.95	$187.90
Purchase #3	$117.34	12.559%	$132.0767	$132.08	$132.10	$132.10
Purchase #4	$179.36	4.327%	$187.1209	$187.12	$187.10	$187.10
Purchase #5	$227.62	12.461%	$255.9837	$255.98	$256.00	$256.00
Purchase #6	$78.95	8.168%	$85.3986	$85.40	$85.40	$85.40
Purchase #7	$41.73	13.826%	$47.4996	$47.50	$47.50	$47.50
7 purchase totals =	$866.85		$940.5302	$940.53	$940.55	$940.50