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	$130.37	10.619%	$144.214	$144.21	$144.20	$144.20
Purchase #2	$236.63	13.495%	$268.5632	$268.56	$268.55	$268.60
Purchase #3	$179.44	4.500%	$187.5148	$187.51	$187.50	$187.50
Purchase #4	$62.94	5.742%	$66.554	$66.55	$66.55	$66.60
Purchase #5	$63.31	13.740%	$72.0088	$72.01	$72.00	$72.00
Purchase #6	$133.94	6.454%	$142.5845	$142.58	$142.60	$142.60
Purchase #7	$28.54	11.643%	$31.8629	$31.86	$31.85	$31.90
7 purchase totals =	$835.17		$913.3022	$913.28	$913.25	$913.40