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	$226.33	13.641%	$257.2037	$257.20	$257.20	$257.20
Purchase #2	$29.59	10.767%	$32.776	$32.78	$32.80	$32.80
Purchase #3	$36.97	5.597%	$39.0392	$39.04	$39.05	$39.00
Purchase #4	$173.59	6.801%	$185.3959	$185.40	$185.40	$185.40
Purchase #5	$134.44	11.866%	$150.3927	$150.39	$150.40	$150.40
Purchase #6	$99.33	12.305%	$111.5526	$111.55	$111.55	$111.60
Purchase #7	$198.79	12.741%	$224.1178	$224.12	$224.10	$224.10
7 purchase totals =	$899.04		$1,000.4779	$1,000.48	$1,000.50	$1,000.50