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	$166.81	3.741%	$173.0504	$173.05	$173.05	$173.10
Purchase #2	$122.55	11.253%	$136.3406	$136.34	$136.35	$136.30
Purchase #3	$100.31	12.198%	$112.5458	$112.55	$112.55	$112.50
Purchase #4	$240.92	9.452%	$263.6918	$263.69	$263.70	$263.70
Purchase #5	$45.72	8.387%	$49.5545	$49.55	$49.55	$49.60
Purchase #6	$83.76	6.837%	$89.4867	$89.49	$89.50	$89.50
Purchase #7	$157.86	5.220%	$166.1003	$166.10	$166.10	$166.10
7 purchase totals =	$917.93		$990.7701	$990.77	$990.80	$990.80