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	$79.73	3.343%	$82.3954	$82.40	$82.40	$82.40
Purchase #2	$184.68	11.624%	$206.1472	$206.15	$206.15	$206.10
Purchase #3	$173.43	7.574%	$186.5656	$186.57	$186.55	$186.60
Purchase #4	$80.78	11.606%	$90.1553	$90.16	$90.15	$90.20
Purchase #5	$10.51	4.366%	$10.9689	$10.97	$10.95	$11.00
Purchase #6	$97.68	13.122%	$110.4976	$110.50	$110.50	$110.50
Purchase #7	$182.63	7.351%	$196.0551	$196.06	$196.05	$196.10
7 purchase totals =	$809.44		$882.7851	$882.81	$882.75	$882.90