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	$135.31	12.257%	$151.8949	$151.89	$151.90	$151.90
Purchase #2	$89.27	11.384%	$99.4325	$99.43	$99.45	$99.40
Purchase #3	$93.77	3.709%	$97.2479	$97.25	$97.25	$97.20
Purchase #4	$21.31	12.115%	$23.8917	$23.89	$23.90	$23.90
Purchase #5	$103.65	3.463%	$107.2394	$107.24	$107.25	$107.20
Purchase #6	$42.85	4.737%	$44.8798	$44.88	$44.90	$44.90
Purchase #7	$250.42	13.591%	$284.4546	$284.45	$284.45	$284.50
7 purchase totals =	$736.58		$809.0408	$809.03	$809.10	$809.00