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	$238.90	11.440%	$266.2302	$266.23	$266.25	$266.20
Purchase #2	$107.84	6.374%	$114.7137	$114.71	$114.70	$114.70
Purchase #3	$62.75	7.156%	$67.2404	$67.24	$67.25	$67.20
Purchase #4	$134.73	4.441%	$140.7134	$140.71	$140.70	$140.70
Purchase #5	$131.27	9.854%	$144.2053	$144.21	$144.20	$144.20
Purchase #6	$184.94	6.370%	$196.7207	$196.72	$196.70	$196.70
Purchase #7	$63.94	10.717%	$70.7924	$70.79	$70.80	$70.80
7 purchase totals =	$924.37		$1,000.6161	$1,000.61	$1,000.60	$1,000.50