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	$27.51	12.748%	$31.017	$31.02	$31.00	$31.00
Purchase #2	$115.33	11.510%	$128.6045	$128.60	$128.60	$128.60
Purchase #3	$188.88	12.110%	$211.7534	$211.75	$211.75	$211.80
Purchase #4	$186.57	5.387%	$196.6205	$196.62	$196.60	$196.60
Purchase #5	$110.60	3.254%	$114.1989	$114.20	$114.20	$114.20
Purchase #6	$42.85	11.189%	$47.6445	$47.64	$47.65	$47.60
Purchase #7	$105.37	6.658%	$112.3855	$112.39	$112.40	$112.40
7 purchase totals =	$777.11		$842.2243	$842.22	$842.20	$842.20