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	$227.66	12.247%	$255.5415	$255.54	$255.55	$255.50
Purchase #2	$205.95	10.507%	$227.5892	$227.59	$227.60	$227.60
Purchase #3	$227.32	12.563%	$255.8782	$255.88	$255.90	$255.90
Purchase #4	$204.74	5.852%	$216.7214	$216.72	$216.70	$216.70
Purchase #5	$206.73	6.294%	$219.7416	$219.74	$219.75	$219.70
Purchase #6	$62.34	11.503%	$69.511	$69.51	$69.50	$69.50
Purchase #7	$39.87	9.649%	$43.7171	$43.72	$43.70	$43.70
7 purchase totals =	$1,174.61		$1,288.7000	$1,288.70	$1,288.70	$1,288.60