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	$133.88	12.138%	$150.1304	$150.13	$150.15	$150.10
Purchase #2	$248.29	12.853%	$280.2027	$280.20	$280.20	$280.20
Purchase #3	$134.30	9.213%	$146.6731	$146.67	$146.65	$146.70
Purchase #4	$48.70	6.212%	$51.7252	$51.73	$51.75	$51.70
Purchase #5	$139.42	4.765%	$146.0634	$146.06	$146.05	$146.10
Purchase #6	$145.93	5.456%	$153.8919	$153.89	$153.90	$153.90
Purchase #7	$40.79	5.108%	$42.8736	$42.87	$42.85	$42.90
7 purchase totals =	$891.31		$971.5603	$971.55	$971.55	$971.60