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	$215.33	11.280%	$239.6192	$239.62	$239.60	$239.60
Purchase #2	$53.34	8.630%	$57.9432	$57.94	$57.95	$57.90
Purchase #3	$213.86	5.864%	$226.4008	$226.40	$226.40	$226.40
Purchase #4	$127.50	12.200%	$143.055	$143.06	$143.05	$143.10
Purchase #5	$82.25	9.780%	$90.2941	$90.29	$90.30	$90.30
Purchase #6	$36.85	7.307%	$39.5426	$39.54	$39.55	$39.50
Purchase #7	$180.39	7.794%	$194.4496	$194.45	$194.45	$194.40
7 purchase totals =	$909.52		$991.3045	$991.30	$991.30	$991.20