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	$28.60	10.575%	$31.6245	$31.62	$31.60	$31.60
Purchase #2	$233.52	11.361%	$260.0502	$260.05	$260.05	$260.10
Purchase #3	$132.41	6.365%	$140.8379	$140.84	$140.85	$140.80
Purchase #4	$90.51	9.276%	$98.9057	$98.91	$98.90	$98.90
Purchase #5	$88.37	8.418%	$95.809	$95.81	$95.80	$95.80
Purchase #6	$205.99	13.132%	$233.0406	$233.04	$233.05	$233.00
Purchase #7	$158.88	6.112%	$168.5907	$168.59	$168.60	$168.60
7 purchase totals =	$938.28		$1,028.8586	$1,028.86	$1,028.85	$1,028.80