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	$69.50	12.417%	$78.1298	$78.13	$78.15	$78.10
Purchase #2	$52.50	8.471%	$56.9473	$56.95	$56.95	$56.90
Purchase #3	$131.72	5.855%	$139.4322	$139.43	$139.45	$139.40
Purchase #4	$35.53	8.334%	$38.4911	$38.49	$38.50	$38.50
Purchase #5	$119.66	6.575%	$127.5276	$127.53	$127.55	$127.50
Purchase #6	$227.43	6.597%	$242.4336	$242.43	$242.45	$242.40
Purchase #7	$90.53	3.491%	$93.6904	$93.69	$93.70	$93.70
7 purchase totals =	$726.87		$776.6520	$776.65	$776.75	$776.50