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	$45.67	10.577%	$50.5005	$50.50	$50.50	$50.50
Purchase #2	$64.49	9.503%	$70.6185	$70.62	$70.60	$70.60
Purchase #3	$160.83	13.643%	$182.772	$182.77	$182.75	$182.80
Purchase #4	$105.51	10.425%	$116.5094	$116.51	$116.50	$116.50
Purchase #5	$51.88	9.353%	$56.7323	$56.73	$56.75	$56.70
Purchase #6	$175.38	4.631%	$183.5018	$183.50	$183.50	$183.50
Purchase #7	$83.35	12.666%	$93.9071	$93.91	$93.90	$93.90
7 purchase totals =	$687.11		$754.5416	$754.54	$754.50	$754.50