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	$74.66	8.393%	$80.9262	$80.93	$80.95	$80.90
Purchase #2	$90.66	11.289%	$100.8946	$100.89	$100.90	$100.90
Purchase #3	$191.93	7.172%	$205.6952	$205.70	$205.70	$205.70
Purchase #4	$117.64	5.844%	$124.5149	$124.51	$124.50	$124.50
Purchase #5	$171.86	6.719%	$183.4073	$183.41	$183.40	$183.40
Purchase #6	$100.43	7.622%	$108.0848	$108.08	$108.10	$108.10
Purchase #7	$37.42	13.285%	$42.3912	$42.39	$42.40	$42.40
7 purchase totals =	$784.60		$845.9142	$845.91	$845.95	$845.90