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	$78.89	13.565%	$89.5914	$89.59	$89.60	$89.60
Purchase #2	$177.70	8.280%	$192.4136	$192.41	$192.40	$192.40
Purchase #3	$157.57	4.601%	$164.8198	$164.82	$164.80	$164.80
Purchase #4	$13.75	11.824%	$15.3758	$15.38	$15.40	$15.40
Purchase #5	$12.71	10.384%	$14.0298	$14.03	$14.05	$14.00
Purchase #6	$77.31	9.515%	$84.666	$84.67	$84.65	$84.70
Purchase #7	$93.61	7.311%	$100.4538	$100.45	$100.45	$100.50
7 purchase totals =	$611.54		$661.3502	$661.35	$661.35	$661.40