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	$232.46	9.488%	$254.5158	$254.52	$254.50	$254.50
Purchase #2	$117.59	11.588%	$131.2163	$131.22	$131.20	$131.20
Purchase #3	$135.77	8.162%	$146.8515	$146.85	$146.85	$146.90
Purchase #4	$35.84	6.398%	$38.133	$38.13	$38.15	$38.10
Purchase #5	$63.59	13.225%	$71.9998	$72.00	$72.00	$72.00
Purchase #6	$211.52	5.386%	$222.9125	$222.91	$222.90	$222.90
Purchase #7	$51.51	3.792%	$53.4633	$53.46	$53.45	$53.50
7 purchase totals =	$848.28		$919.0922	$919.09	$919.05	$919.10