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	$95.66	12.416%	$107.5371	$107.54	$107.55	$107.50
Purchase #2	$178.94	11.809%	$200.071	$200.07	$200.05	$200.10
Purchase #3	$71.62	9.670%	$78.5457	$78.55	$78.55	$78.50
Purchase #4	$108.44	4.142%	$112.9316	$112.93	$112.95	$112.90
Purchase #5	$18.35	13.143%	$20.7617	$20.76	$20.75	$20.80
Purchase #6	$72.77	7.869%	$78.4963	$78.50	$78.50	$78.50
Purchase #7	$211.85	13.146%	$239.6998	$239.70	$239.70	$239.70
7 purchase totals =	$757.63		$838.0432	$838.05	$838.05	$838.00