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	$248.56	3.153%	$256.3971	$256.40	$256.40	$256.40
Purchase #2	$184.46	8.783%	$200.6611	$200.66	$200.65	$200.70
Purchase #3	$70.62	11.338%	$78.6269	$78.63	$78.65	$78.60
Purchase #4	$170.87	10.250%	$188.3842	$188.38	$188.40	$188.40
Purchase #5	$126.87	8.533%	$137.6958	$137.70	$137.70	$137.70
Purchase #6	$140.81	9.233%	$153.811	$153.81	$153.80	$153.80
Purchase #7	$54.37	12.787%	$61.3223	$61.32	$61.30	$61.30
7 purchase totals =	$996.56		$1,076.8984	$1,076.90	$1,076.90	$1,076.90