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	$128.73	12.263%	$144.5162	$144.52	$144.50	$144.50
Purchase #2	$51.77	7.702%	$55.7573	$55.76	$55.75	$55.80
Purchase #3	$33.31	12.627%	$37.5161	$37.52	$37.50	$37.50
Purchase #4	$48.26	5.850%	$51.0832	$51.08	$51.10	$51.10
Purchase #5	$211.26	10.793%	$234.0613	$234.06	$234.05	$234.10
Purchase #6	$12.27	11.612%	$13.6948	$13.69	$13.70	$13.70
Purchase #7	$172.56	5.226%	$181.578	$181.58	$181.60	$181.60
7 purchase totals =	$658.16		$718.2069	$718.21	$718.20	$718.30