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	$76.72	7.481%	$82.4594	$82.46	$82.45	$82.50
Purchase #2	$35.46	13.336%	$40.1889	$40.19	$40.20	$40.20
Purchase #3	$167.60	5.328%	$176.5297	$176.53	$176.55	$176.50
Purchase #4	$57.69	12.583%	$64.9491	$64.95	$64.95	$64.90
Purchase #5	$248.97	8.252%	$269.515	$269.52	$269.50	$269.50
Purchase #6	$49.92	10.303%	$55.0633	$55.06	$55.05	$55.10
Purchase #7	$119.78	11.309%	$133.3259	$133.33	$133.35	$133.30
7 purchase totals =	$756.14		$822.0313	$822.04	$822.05	$822.00