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	$44.98	6.453%	$47.8826	$47.88	$47.90	$47.90
Purchase #2	$239.33	11.358%	$266.5131	$266.51	$266.50	$266.50
Purchase #3	$207.89	3.789%	$215.767	$215.77	$215.75	$215.80
Purchase #4	$10.45	8.359%	$11.3235	$11.32	$11.30	$11.30
Purchase #5	$30.81	8.587%	$33.4557	$33.46	$33.45	$33.50
Purchase #6	$145.93	3.775%	$151.4389	$151.44	$151.45	$151.40
Purchase #7	$33.50	13.609%	$38.059	$38.06	$38.05	$38.10
7 purchase totals =	$712.89		$764.4398	$764.44	$764.40	$764.50