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	$51.65	5.556%	$54.5197	$54.52	$54.50	$54.50
Purchase #2	$216.59	9.839%	$237.9003	$237.90	$237.90	$237.90
Purchase #3	$97.77	5.179%	$102.8335	$102.83	$102.85	$102.80
Purchase #4	$160.95	12.414%	$180.9303	$180.93	$180.95	$180.90
Purchase #5	$87.44	9.248%	$95.5265	$95.53	$95.55	$95.50
Purchase #6	$110.82	11.527%	$123.5942	$123.59	$123.60	$123.60
Purchase #7	$152.68	6.528%	$162.647	$162.65	$162.65	$162.60
7 purchase totals =	$877.90		$957.9515	$957.95	$958.00	$957.80