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	$74.72	5.263%	$78.6525	$78.65	$78.65	$78.70
Purchase #2	$141.87	8.608%	$154.0822	$154.08	$154.10	$154.10
Purchase #3	$85.62	10.558%	$94.6598	$94.66	$94.65	$94.70
Purchase #4	$143.27	10.626%	$158.4939	$158.49	$158.50	$158.50
Purchase #5	$192.69	4.131%	$200.65	$200.65	$200.65	$200.70
Purchase #6	$109.60	8.575%	$118.9982	$119.00	$119.00	$119.00
Purchase #7	$111.78	12.728%	$126.0074	$126.01	$126.00	$126.00
7 purchase totals =	$859.55		$931.5440	$931.54	$931.55	$931.70