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	$82.26	8.202%	$89.007	$89.01	$89.00	$89.00
Purchase #2	$173.25	8.124%	$187.3248	$187.32	$187.30	$187.30
Purchase #3	$238.46	13.698%	$271.1243	$271.12	$271.10	$271.10
Purchase #4	$18.46	13.764%	$21.0008	$21.00	$21.00	$21.00
Purchase #5	$182.52	4.565%	$190.852	$190.85	$190.85	$190.90
Purchase #6	$191.61	12.622%	$215.795	$215.80	$215.80	$215.80
Purchase #7	$162.58	9.360%	$177.7975	$177.80	$177.80	$177.80
7 purchase totals =	$1,049.14		$1,152.9014	$1,152.90	$1,152.85	$1,152.90