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	$29.76	5.822%	$31.4926	$31.49	$31.50	$31.50
Purchase #2	$32.91	8.786%	$35.8015	$35.80	$35.80	$35.80
Purchase #3	$58.47	7.531%	$62.8734	$62.87	$62.85	$62.90
Purchase #4	$19.61	10.723%	$21.7128	$21.71	$21.70	$21.70
Purchase #5	$242.95	5.179%	$255.5324	$255.53	$255.55	$255.50
Purchase #6	$159.50	10.611%	$176.4245	$176.42	$176.40	$176.40
Purchase #7	$163.83	10.549%	$181.1124	$181.11	$181.10	$181.10
7 purchase totals =	$707.03		$764.9496	$764.93	$764.90	$764.90