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	$40.70	4.280%	$42.442	$42.44	$42.45	$42.40
Purchase #2	$239.94	13.387%	$272.0608	$272.06	$272.05	$272.10
Purchase #3	$32.77	13.623%	$37.2343	$37.23	$37.25	$37.20
Purchase #4	$92.97	5.864%	$98.4218	$98.42	$98.40	$98.40
Purchase #5	$197.27	8.448%	$213.9354	$213.94	$213.95	$213.90
Purchase #6	$74.83	10.561%	$82.7328	$82.73	$82.75	$82.70
Purchase #7	$190.44	10.450%	$210.341	$210.34	$210.35	$210.30
7 purchase totals =	$868.92		$957.1681	$957.16	$957.20	$957.00