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	$123.40	12.249%	$138.5153	$138.52	$138.50	$138.50
Purchase #2	$121.60	12.480%	$136.7757	$136.78	$136.80	$136.80
Purchase #3	$123.44	3.233%	$127.4308	$127.43	$127.45	$127.40
Purchase #4	$183.70	6.869%	$196.3184	$196.32	$196.30	$196.30
Purchase #5	$245.32	13.117%	$277.4986	$277.50	$277.50	$277.50
Purchase #6	$110.96	5.395%	$116.9463	$116.95	$116.95	$116.90
Purchase #7	$156.91	11.774%	$175.3846	$175.38	$175.40	$175.40
7 purchase totals =	$1,065.33		$1,168.8697	$1,168.88	$1,168.90	$1,168.80