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	$70.34	8.709%	$76.4659	$76.47	$76.45	$76.50
Purchase #2	$38.32	4.130%	$39.9026	$39.90	$39.90	$39.90
Purchase #3	$188.64	5.268%	$198.5776	$198.58	$198.60	$198.60
Purchase #4	$54.34	4.619%	$56.85	$56.85	$56.85	$56.90
Purchase #5	$41.44	4.667%	$43.374	$43.37	$43.35	$43.40
Purchase #6	$107.66	6.765%	$114.9432	$114.94	$114.95	$114.90
Purchase #7	$10.42	7.472%	$11.1986	$11.20	$11.20	$11.20
7 purchase totals =	$511.16		$541.3119	$541.31	$541.30	$541.40