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	$91.28	10.254%	$100.6399	$100.64	$100.65	$100.60
Purchase #2	$159.52	6.235%	$169.4661	$169.47	$169.45	$169.50
Purchase #3	$154.84	4.642%	$162.0277	$162.03	$162.05	$162.00
Purchase #4	$30.25	8.131%	$32.7096	$32.71	$32.70	$32.70
Purchase #5	$235.88	12.652%	$265.7235	$265.72	$265.70	$265.70
Purchase #6	$102.66	8.160%	$111.0371	$111.04	$111.05	$111.00
Purchase #7	$107.83	10.413%	$119.0583	$119.06	$119.05	$119.10
7 purchase totals =	$882.26		$960.6622	$960.67	$960.65	$960.60