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	$87.97	3.314%	$90.8853	$90.89	$90.90	$90.90
Purchase #2	$34.29	13.304%	$38.8519	$38.85	$38.85	$38.90
Purchase #3	$126.70	6.455%	$134.8785	$134.88	$134.90	$134.90
Purchase #4	$250.29	13.502%	$284.0842	$284.08	$284.10	$284.10
Purchase #5	$107.86	13.363%	$122.2733	$122.27	$122.25	$122.30
Purchase #6	$29.39	5.678%	$31.0588	$31.06	$31.05	$31.10
Purchase #7	$183.71	4.774%	$192.4803	$192.48	$192.50	$192.50
7 purchase totals =	$820.21		$894.5123	$894.51	$894.55	$894.70