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	$134.40	13.697%	$152.8088	$152.81	$152.80	$152.80
Purchase #2	$210.73	13.795%	$239.8002	$239.80	$239.80	$239.80
Purchase #3	$171.54	9.499%	$187.8346	$187.83	$187.85	$187.80
Purchase #4	$223.50	10.337%	$246.6032	$246.60	$246.60	$246.60
Purchase #5	$179.56	3.238%	$185.3742	$185.37	$185.35	$185.40
Purchase #6	$225.54	12.310%	$253.304	$253.30	$253.30	$253.30
Purchase #7	$52.89	3.683%	$54.8379	$54.84	$54.85	$54.80
7 purchase totals =	$1,198.16		$1,320.5629	$1,320.55	$1,320.55	$1,320.50