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	$50.51	6.477%	$53.7815	$53.78	$53.80	$53.80
Purchase #2	$106.61	7.394%	$114.4927	$114.49	$114.50	$114.50
Purchase #3	$244.64	12.810%	$275.9784	$275.98	$276.00	$276.00
Purchase #4	$37.84	12.609%	$42.6112	$42.61	$42.60	$42.60
Purchase #5	$112.85	12.431%	$126.8784	$126.88	$126.90	$126.90
Purchase #6	$57.52	10.217%	$63.3968	$63.40	$63.40	$63.40
Purchase #7	$223.67	12.359%	$251.3134	$251.31	$251.30	$251.30
7 purchase totals =	$833.64		$928.4524	$928.45	$928.50	$928.50