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	$250.49	3.416%	$259.0467	$259.05	$259.05	$259.00
Purchase #2	$181.45	3.621%	$188.0203	$188.02	$188.00	$188.00
Purchase #3	$238.93	8.607%	$259.4947	$259.49	$259.50	$259.50
Purchase #4	$91.90	12.558%	$103.4408	$103.44	$103.45	$103.40
Purchase #5	$228.66	13.335%	$259.1518	$259.15	$259.15	$259.20
Purchase #6	$78.76	4.845%	$82.5759	$82.58	$82.60	$82.60
Purchase #7	$218.35	6.730%	$233.045	$233.05	$233.05	$233.00
7 purchase totals =	$1,288.54		$1,384.7752	$1,384.78	$1,384.80	$1,384.70