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	$61.43	6.194%	$65.235	$65.24	$65.25	$65.20
Purchase #2	$43.77	10.820%	$48.5059	$48.51	$48.50	$48.50
Purchase #3	$196.52	13.721%	$223.4845	$223.48	$223.50	$223.50
Purchase #4	$124.32	10.601%	$137.4992	$137.50	$137.50	$137.50
Purchase #5	$166.51	6.644%	$177.5729	$177.57	$177.55	$177.60
Purchase #6	$228.32	12.523%	$256.9125	$256.91	$256.90	$256.90
Purchase #7	$84.51	5.193%	$88.8986	$88.90	$88.90	$88.90
7 purchase totals =	$905.38		$998.1086	$998.11	$998.10	$998.10