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	$137.98	4.733%	$144.5106	$144.51	$144.50	$144.50
Purchase #2	$144.57	4.440%	$150.9889	$150.99	$151.00	$151.00
Purchase #3	$224.80	13.793%	$255.8067	$255.81	$255.80	$255.80
Purchase #4	$204.57	11.535%	$228.1671	$228.17	$228.15	$228.20
Purchase #5	$170.54	9.347%	$186.4804	$186.48	$186.50	$186.50
Purchase #6	$35.35	10.821%	$39.1752	$39.18	$39.20	$39.20
Purchase #7	$157.86	10.725%	$174.7905	$174.79	$174.80	$174.80
7 purchase totals =	$1,075.67		$1,179.9194	$1,179.93	$1,179.95	$1,180.00