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	$248.52	7.693%	$267.6386	$267.64	$267.65	$267.60
Purchase #2	$111.76	13.227%	$126.5425	$126.54	$126.55	$126.50
Purchase #3	$31.67	7.578%	$34.07	$34.07	$34.05	$34.10
Purchase #4	$23.72	7.309%	$25.4537	$25.45	$25.45	$25.50
Purchase #5	$155.32	7.857%	$167.5235	$167.52	$167.50	$167.50
Purchase #6	$232.86	9.706%	$255.4614	$255.46	$255.45	$255.50
Purchase #7	$104.98	11.400%	$116.9477	$116.95	$116.95	$116.90
7 purchase totals =	$908.83		$993.6374	$993.63	$993.60	$993.60