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	$29.90	6.453%	$31.8294	$31.83	$31.85	$31.80
Purchase #2	$146.59	9.588%	$160.645	$160.65	$160.65	$160.60
Purchase #3	$85.57	5.797%	$90.5305	$90.53	$90.55	$90.50
Purchase #4	$166.25	9.225%	$181.5866	$181.59	$181.60	$181.60
Purchase #5	$144.39	10.873%	$160.0895	$160.09	$160.10	$160.10
Purchase #6	$12.88	5.791%	$13.6259	$13.63	$13.65	$13.60
Purchase #7	$33.58	12.587%	$37.8067	$37.81	$37.80	$37.80
7 purchase totals =	$619.16		$676.1136	$676.13	$676.20	$676.00