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	$240.71	8.776%	$261.8347	$261.83	$261.85	$261.80
Purchase #2	$160.25	9.134%	$174.8872	$174.89	$174.90	$174.90
Purchase #3	$18.88	12.660%	$21.2702	$21.27	$21.25	$21.30
Purchase #4	$171.35	11.109%	$190.3853	$190.39	$190.40	$190.40
Purchase #5	$154.43	12.839%	$174.2573	$174.26	$174.25	$174.30
Purchase #6	$76.90	9.150%	$83.9364	$83.94	$83.95	$83.90
Purchase #7	$20.60	3.857%	$21.3945	$21.39	$21.40	$21.40
7 purchase totals =	$843.12		$927.9656	$927.97	$928.00	$928.00