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	$139.68	12.290%	$156.8467	$156.85	$156.85	$156.80
Purchase #2	$245.30	8.756%	$266.7785	$266.78	$266.80	$266.80
Purchase #3	$131.38	10.810%	$145.5822	$145.58	$145.60	$145.60
Purchase #4	$233.87	11.361%	$260.44	$260.44	$260.45	$260.40
Purchase #5	$114.78	8.432%	$124.4582	$124.46	$124.45	$124.50
Purchase #6	$27.64	12.149%	$30.998	$31.00	$31.00	$31.00
Purchase #7	$29.31	7.332%	$31.459	$31.46	$31.45	$31.50
7 purchase totals =	$921.96		$1,016.5626	$1,016.57	$1,016.60	$1,016.60