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	$124.30	8.534%	$134.9078	$134.91	$134.90	$134.90
Purchase #2	$51.46	9.706%	$56.4547	$56.45	$56.45	$56.50
Purchase #3	$236.58	12.272%	$265.6131	$265.61	$265.60	$265.60
Purchase #4	$208.70	7.680%	$224.7282	$224.73	$224.75	$224.70
Purchase #5	$169.48	9.463%	$185.5179	$185.52	$185.50	$185.50
Purchase #6	$136.93	12.166%	$153.5889	$153.59	$153.60	$153.60
Purchase #7	$49.78	11.263%	$55.3867	$55.39	$55.40	$55.40
7 purchase totals =	$977.23		$1,076.1973	$1,076.20	$1,076.20	$1,076.20