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	$73.27	6.499%	$78.0318	$78.03	$78.05	$78.00
Purchase #2	$100.81	13.570%	$114.4899	$114.49	$114.50	$114.50
Purchase #3	$69.47	6.462%	$73.9592	$73.96	$73.95	$74.00
Purchase #4	$129.76	3.619%	$134.456	$134.46	$134.45	$134.50
Purchase #5	$18.67	13.841%	$21.2541	$21.25	$21.25	$21.30
Purchase #6	$249.89	7.236%	$267.972	$267.97	$267.95	$268.00
Purchase #7	$128.60	11.367%	$143.218	$143.22	$143.20	$143.20
7 purchase totals =	$770.47		$833.3810	$833.38	$833.35	$833.50