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	$21.70	5.764%	$22.9508	$22.95	$22.95	$23.00
Purchase #2	$170.94	12.355%	$192.0596	$192.06	$192.05	$192.10
Purchase #3	$26.43	6.757%	$28.2159	$28.22	$28.20	$28.20
Purchase #4	$76.53	7.260%	$82.0861	$82.09	$82.10	$82.10
Purchase #5	$214.46	5.327%	$225.8843	$225.88	$225.90	$225.90
Purchase #6	$12.90	5.109%	$13.5591	$13.56	$13.55	$13.60
Purchase #7	$101.61	3.422%	$105.0871	$105.09	$105.10	$105.10
7 purchase totals =	$624.57		$669.8429	$669.85	$669.85	$670.00