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	$125.76	11.709%	$140.4852	$140.49	$140.50	$140.50
Purchase #2	$38.28	11.602%	$42.7212	$42.72	$42.70	$42.70
Purchase #3	$116.54	12.448%	$131.0469	$131.05	$131.05	$131.00
Purchase #4	$128.91	8.425%	$139.7707	$139.77	$139.75	$139.80
Purchase #5	$35.86	9.140%	$39.1376	$39.14	$39.15	$39.10
Purchase #6	$8.86	9.823%	$9.7303	$9.73	$9.75	$9.70
Purchase #7	$215.86	8.164%	$233.4828	$233.48	$233.50	$233.50
7 purchase totals =	$670.07		$736.3747	$736.38	$736.40	$736.30