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	$38.61	10.738%	$42.7559	$42.76	$42.75	$42.80
Purchase #2	$213.74	7.231%	$229.1955	$229.20	$229.20	$229.20
Purchase #3	$51.41	6.657%	$54.8324	$54.83	$54.85	$54.80
Purchase #4	$60.81	9.715%	$66.7177	$66.72	$66.70	$66.70
Purchase #5	$33.46	9.146%	$36.5203	$36.52	$36.50	$36.50
Purchase #6	$176.93	11.304%	$196.9302	$196.93	$196.95	$196.90
Purchase #7	$143.51	5.385%	$151.238	$151.24	$151.25	$151.20
7 purchase totals =	$718.47		$778.1900	$778.20	$778.20	$778.10