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	$37.75	4.159%	$39.32	$39.32	$39.30	$39.30
Purchase #2	$202.89	12.616%	$228.4866	$228.49	$228.50	$228.50
Purchase #3	$237.28	7.826%	$255.8495	$255.85	$255.85	$255.80
Purchase #4	$126.79	4.524%	$132.526	$132.53	$132.55	$132.50
Purchase #5	$231.87	10.391%	$255.9636	$255.96	$255.95	$256.00
Purchase #6	$136.67	12.248%	$153.4093	$153.41	$153.40	$153.40
Purchase #7	$89.83	3.145%	$92.6552	$92.66	$92.65	$92.70
7 purchase totals =	$1,063.08		$1,158.2102	$1,158.22	$1,158.20	$1,158.20