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	$105.40	13.193%	$119.3054	$119.31	$119.30	$119.30
Purchase #2	$68.96	4.414%	$72.0039	$72.00	$72.00	$72.00
Purchase #3	$56.25	8.660%	$61.1213	$61.12	$61.10	$61.10
Purchase #4	$216.93	3.492%	$224.5052	$224.51	$224.50	$224.50
Purchase #5	$80.63	11.245%	$89.6968	$89.70	$89.70	$89.70
Purchase #6	$150.45	12.852%	$169.7858	$169.79	$169.80	$169.80
Purchase #7	$144.52	13.264%	$163.6891	$163.69	$163.70	$163.70
7 purchase totals =	$823.14		$900.1075	$900.12	$900.10	$900.10