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	$21.45	9.854%	$23.5637	$23.56	$23.55	$23.60
Purchase #2	$192.41	13.206%	$217.8197	$217.82	$217.80	$217.80
Purchase #3	$235.97	10.619%	$261.0277	$261.03	$261.05	$261.00
Purchase #4	$98.38	13.364%	$111.5275	$111.53	$111.55	$111.50
Purchase #5	$202.69	9.636%	$222.2212	$222.22	$222.20	$222.20
Purchase #6	$55.79	11.795%	$62.3704	$62.37	$62.35	$62.40
Purchase #7	$83.98	6.244%	$89.2237	$89.22	$89.20	$89.20
7 purchase totals =	$890.67		$987.7539	$987.75	$987.70	$987.70