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	$24.30	13.344%	$27.5426	$27.54	$27.55	$27.50
Purchase #2	$77.88	6.367%	$82.8386	$82.84	$82.85	$82.80
Purchase #3	$123.98	12.808%	$139.8594	$139.86	$139.85	$139.90
Purchase #4	$19.54	11.254%	$21.739	$21.74	$21.75	$21.70
Purchase #5	$52.88	5.592%	$55.837	$55.84	$55.85	$55.80
Purchase #6	$65.92	13.315%	$74.6972	$74.70	$74.70	$74.70
Purchase #7	$128.87	11.605%	$143.8254	$143.83	$143.85	$143.80
7 purchase totals =	$493.37		$546.3392	$546.35	$546.40	$546.20