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	$127.45	5.745%	$134.772	$134.77	$134.75	$134.80
Purchase #2	$70.88	13.586%	$80.5098	$80.51	$80.50	$80.50
Purchase #3	$46.46	9.791%	$51.0089	$51.01	$51.00	$51.00
Purchase #4	$135.73	12.857%	$153.1808	$153.18	$153.20	$153.20
Purchase #5	$249.95	12.390%	$280.9188	$280.92	$280.90	$280.90
Purchase #6	$145.90	6.827%	$155.8606	$155.86	$155.85	$155.90
Purchase #7	$134.62	8.869%	$146.5594	$146.56	$146.55	$146.60
7 purchase totals =	$910.99		$1,002.8103	$1,002.81	$1,002.75	$1,002.90