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	$186.88	3.244%	$192.9424	$192.94	$192.95	$192.90
Purchase #2	$246.98	13.331%	$279.9049	$279.90	$279.90	$279.90
Purchase #3	$201.46	8.397%	$218.3766	$218.38	$218.40	$218.40
Purchase #4	$49.79	13.526%	$56.5246	$56.52	$56.50	$56.50
Purchase #5	$195.84	11.256%	$217.8838	$217.88	$217.90	$217.90
Purchase #6	$18.55	10.514%	$20.5003	$20.50	$20.50	$20.50
Purchase #7	$157.98	9.739%	$173.3657	$173.37	$173.35	$173.40
7 purchase totals =	$1,057.48		$1,159.4983	$1,159.49	$1,159.50	$1,159.50