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	$203.70	3.348%	$210.5199	$210.52	$210.50	$210.50
Purchase #2	$18.60	9.741%	$20.4118	$20.41	$20.40	$20.40
Purchase #3	$45.57	12.513%	$51.2722	$51.27	$51.25	$51.30
Purchase #4	$172.77	10.487%	$190.8884	$190.89	$190.90	$190.90
Purchase #5	$8.72	7.404%	$9.3656	$9.37	$9.35	$9.40
Purchase #6	$108.93	12.377%	$122.4123	$122.41	$122.40	$122.40
Purchase #7	$81.39	9.704%	$89.2881	$89.29	$89.30	$89.30
7 purchase totals =	$639.68		$694.1583	$694.16	$694.10	$694.20