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	$111.43	8.206%	$120.5739	$120.57	$120.55	$120.60
Purchase #2	$232.37	10.572%	$256.9362	$256.94	$256.95	$256.90
Purchase #3	$11.42	3.871%	$11.8621	$11.86	$11.85	$11.90
Purchase #4	$239.72	13.667%	$272.4825	$272.48	$272.50	$272.50
Purchase #5	$128.47	12.314%	$144.2898	$144.29	$144.30	$144.30
Purchase #6	$7.84	3.121%	$8.0847	$8.08	$8.10	$8.10
Purchase #7	$230.73	8.595%	$250.5612	$250.56	$250.55	$250.60
7 purchase totals =	$961.98		$1,064.7904	$1,064.78	$1,064.80	$1,064.90